Since the program doesn't have a function to measure the height of objects that you change using the scale button, the easiest way to measure height is to create a simple horizontal plane. Once you have created a plane, you can alter its altitude to the height you are looking for, then use that as a measure when you alter the height of your other objects as pictured here:

To make a horizontal plane, click on the "Objects" button, then the "Geometries" tab, and drag the 11th object (row 4, column 2) into your blueprint.

Feel free to change this plane to any size that works for you, (I prefer to keep it 2'x3' so I can use the sides as rulers.) You can also change this to any texture or color that contrasts well, or use "Tile" textures to divide it evenly (more detailed description on using tile textures in the next section.)

Note that the plane is 1" thick. This means we can change the altitude of the plane to one inch higher than the desired height of whatever object you are editing, so that when you scale the height of your other object while it is positioned under the plane, it should snap to one inch below the altitude of the plane (which is the height you actually want.) (pictured above)

Alternatively you can set the altitude of the plane to the exact height you want, then see if the plane clips into the top of the other object. (pictured below)

Now that you have your measuring device, you can copy it and place one on each floor for convenience.

Next we will make 3D height references by creating perfect cubes.

To create our first cube, click on "Objects", and pick the "Geometries" tab. The first item in the list is a 3'3" cube. Place that object into your house. To make sure that it won't snap to specific sizes on any dimension, be sure to place it away from other objects and walls. Go into 2D mode. Highlight the cube and click on the "scale" button. Use the corner arrow to scale the entire object to exactly 3ft x 3ft x 3ft. Using the corner arrow will scale the height by the same ratio as the sides.

Note that it might not look like a perfect cube for 2 reasons. 1. If you changed the field of view setting to anything other than 60 degrees, which is what the program is automatically set to, the depth and width will be effected by that. 2. Even with the correct field of view it might still look too tall because of the way the angles render in 3D visit mode. If that is the case for you, you can check that it is a perfect cube by raising the cube's altitude to about 3'4" in 3D visit mode and looking at the cube straight on (see the blue highlighted cube in the picture above.)

Once your cube is exactly 3ft in every dimension, click on the "Textures" button, then the "Tiles" button. I chose to texture my cube with the 27th tile texture, which is row 9, column 3, a dark gray 3x3 tile. When you texture your cube, you will notice that the texture divides each side of the cube into an approximate 1'x1' grid (the blue highlighted cube in the picture above.)

Next we will use the same steps as above, but make a 2'x2' cube. Once you have made 2'x2' cube, you can texture it with texture 30, row 10, column 3. That texture will divide your 2'x2' cube into an approximate 1'x1' grid (the bottom left cube in the picture.)

If estimating by the nearest foot isn't good enough for you, you can use the same steps above to create cubes of any size, then use the tile textures to divide your cubes into perfect grids. Note that the tile texture technique works well for this specific cube object, but the texture might not align properly for other objects. For example you could make a 1ft cube and use texture 27 to get 4in squares, or texture 30 to get 6in squares, but the same texture doesn't align exactly with the plane we made in the previous section. The examples in the picture are the bottom middle and bottom right cubes showing a 2ft cube divided by 3x3 tile and a 3ft cube divided by a 2x2 tile respectively.

Alternatively you can search through the list of objects in the program to find something with a similar height to what you are looking for, but be sure that the program isn't including any airspace above the object in its measurement.