Just trying to help other people out that may be struggling to understand how buildings work in Foundation. I'm not trying to judge anyone who's having issues, or dismiss bugs. Also, note I'm not an expert, this is just based on my own play through and discovering how things work, or what worked best for me.

I hope you find this guide useful, I may add more to it over time, I'm still new to Foundation and no doubt there is still more for me to learn as well.

I feel much of the confusion, and bug reports, around Foundation are because players are used to other city building games where you build a production building of some sort, and it already contains all of its requirements within that building.

Let's use Anno 1404 as an example, the developers created the production building, it contains everything that's needed for it to function. You place it, your people construct it, and then all you need to do is ensure it has workers and any raw materials it needs. There's nothing else you need to do. However, these pre-created buildings the developers provide have one problem, you have no control over how they look, this is particularly evident when you look at monument type buildings like the Cathedral or Castle:

(The screenshots are small and not that great, blame steam for not allowing me to attach images that are already in my steam screenshots library but not associated with Foundation, and a pathetic 2GB size limit).

- You have no control over the building itself, you can do some decorating around the outside, but that's all:
https://images.steamusercontent.com/ugc/61466279809463803/B2F46564D24449380B08B3E335D6AA2B077C4746/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

- You can place the various parts of it in any order you like, these are all effectively separate buildings so it doesn't matter what parts you use or don't use:
https://images.steamusercontent.com/ugc/61466279809465905/E8E0D44ADF67E859C5F553B24C334B19FFCCC7BB/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

In Foundation many buildings still work like that, but there are some, particularly monuments, that don't. The positive of this difference is you can control what the final monument looks like, sure, you are using pre-made building parts, but you can use any parts you like and arrange them in any order you like, as long as the building requirements are met.

In the following sections I will explain and demonstrate how to construct monument buildings where all the sub-buildings are combined in one monument.

A Candle Workshop, and Common Wares Workshop with fortification from the Tower. Note each buildings requirements inside the boxes, without fortification these buildings won't function. In this example everything is green, so its working:
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442322536

Here I removed the tower, note the hammer icon indicating an issue, and the red ! inside the box for Candle Workshop, and Common Wares Workshop also indicate its missing a required structure. These buildings can't function in this state.
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442322494

When ever you place a building, any type of building, be sure to check you've met all its requirements or the building won't work.

I'll start with the monastery since for me its the building I've worked on the most so far. You'll see in this first screenshot I click on one part of the monastery, but every sub building is also selected with white outline, including gardens for vegetables, beehives, berries, herbs, etc. So everything is one monastery:
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442312763

Here you can see the monastery, and all of the sub buildings attached to the overall monastery, all listed on the left side. To add more sub buildings, click the + at the bottom of this section, select what type of sub building you want, and then place it. You should see that new sub-building added to this list:
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442283119
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442283099
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442283078

Here is my Castle, again you'll see all sub buildings are selected with white outline, and then when I edit the castle (hammer icon) it lists all the sub-buildings on the left side. You will also note on the right hand side of the edit menu, it lists the buildings requirements, just like the workshops. Also, with this and the Manor House, visually it looks like separate buildings, but they're still part of the same monument even though they aren't physically connected:
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442312828
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442312795

Same again for the Manor House:
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442312884
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442312855

And for the Tavern:
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442312720
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442312684

If you are having problems with a monument, you need to make sure all of its parts are one monument, not lots of individual buildings. If you have a monastery and workers aren't working, its highly likely you've built multiple monasteries rather than one. Edit your monastery, if it only lists one sub-building, eg dorm, that's the problem.

If you prefer, here is a video from youtube showing me building a Manor House with various sub-buildings, adding staff, and then editing the building to add more parts, and decorations:

Note: You don't need to build your manor house the exact same way I've built the one in this video, what sub-buildings you choose is up to you to decide. Also, don't build too big too soon, all this adds to the overall upkeep costs and could have a negative impact on your budget.

You don't assign workers, the monastery does that for you. If you find workers are being pulled off of one task, eg scripture writing, to do beehives, this indicates you don't have enough monks/nuns for all of the available jobs, so the monastery is moving staff around to do a bit of scripture writing, a bit of beehives, a bit of vegetables. Build more dorm space and add more monks/nuns to resolve this. I have 26 nuns, 26 monks, and 52 jobs, so every worker slot is filled, and nobody is idle.

Having watched a few people streaming Foundation, it seems some people get caught up accepting every new villager/migrant that shows up. That's unnecessary, and hurts immigration. Accept as many people as you have jobs for, or will soon have jobs for, you don't want lots of unemployed people hanging around, it means immigration will slow down because nobody wants to come to a town with a lack of employment. For large parts of my game, I've had immigration disabled, I turn it on when I'm expanding and need additional workers, the rest of the time it's disabled. You don't need to disable it, but just because someone new shows up doesn't mean you have to accept.

I've seen some confusion over trading surplus resources, I wasn't 100% sure of it myself until last night when I spent a lot of time playing with these numbers.

When this number (in this example I'm using Bread, but this is true for any resource you want to trade):
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442346376

Exceeds this number:
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442346344

They will begin selling to anyone that comes along willing to buy. In my experience, it does not matter how much you have in storage, as long as the overall total exceeds the limit you set, they begin selling that resource. In this case, when I have over 650 bread, they begin to sell bread, I have 697 bread in total, so they will sell up to 47 bread.

I've seen quite a few people having issues with bridges, as far as I can see from those that posted screenshots of the issue, to me these bridges all look too short. When you drag out the bridge to span the water, or from one cliff to another, it will allow you to build an unusable bridge, clearly a bug at this point in time.

See below 3 examples of bridges side by side, the top one works as it completely spans the water with each end point clearly on land. The other two don't work, at least one end is not completely on land, it can be hard to see even when fully zoomed in, but you can see there are two serfs stuck on the left side of the bottom bridge, that end is slightly in water.
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442517221

Hopefully in the longer term they will fix this issue by either having the tool alert you to the problem, or allowing these shorter bridges to still work.

If you want your village to look as if it was planned, you can use fences to plan out paths/roads for your village. You can place fences along each side of the path/road you want to create, but don't click the "Build" button, instead click the "X" button to close the build window. You will still be able to see the fence, but it isn't built yet, allowing you to later click > edit > and make adjustments to it later on as your settlement grows to accommodate more buildings, or enlarging existing buildings.

You can see here, you'll see fences, but none of these have been built yet. They allow me to know where the edge of the path is, so I can then place buildings along it.

If you ever get errors about a villager being unable to access a certain building, or path being blocked, check this.

When you place buildings to be constructed, you will notice a blue outline around the building, this matters. Avoid having any other object too close to this outline. In the first screenshot, I show the granary and one extension, with a small amount of space in between, this seems to work fine.
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442534065

In this example, I'm placing a storage building, but although Foundation will allow this storage building to be constructed, and even though it may still function correctly, it will still generate errors any time a villager tries to access storage from the right side (red arrow). Chances are it will also cause the granary to generate errors for the same reason.

Also note, that some buildings, like storage, have multiple access points (white arrows are access points that will work, red arrows indicate the access point is blocked). Ensure all access points are white.
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3442534026