Auras & the Buffs(except the right hand sided buff at mid) are placed during the initial build phase. Reflects, physical and any remaining buffs is placed after summoning minions at each crystal during the 2nd wave.
Rest traps and Harpoons and any other remaining towers/minions must be completed by the 3rd wave.
Remember this - if you are trying on solo, you'll have to go DPS and try to save up as much mana as you can during the 1 combat wave. And you'll have to stay DPS during each and every combat wave. Upgrade all the buffs first, starting from West Crystal in a clockwise direction. Max out the Physical at mid, then begin upgrading Auras & Mages(if any) starting from West crystal same procedure as Buffs. Although keep repairing every now and then. By wave 12 or 13 you should be able to max out all Buffs, Auras, Mages and Traps(optional but keep repairing the proxies). Then Max out Archers / Harpoons if you'd like to.
Final wave is 15th, there is no boss. But keep a tab at defenses all the time.

If the buff sizes appear bigger than the provided DU in the screens don't worry just go by the amount of DU mentioned.
If you prefer album view then I've uploaded the images with more details here: http://imgur.com/a/HBr5d#0

Overview:


Mid:



West:



North:



South:

Leave your feedback and/or any other improvement ideas you might have.


<3 Mambo.