I am actually playing the PS1 version of the game, and I have encountered a frustrating problem. I am on Campaign Beta 4, "Urban 4" on my game, and I am working on a base. I was told I reached the structure capacity while I was trying to build a CB radar turret and also when I was trying to create a chain of plain concrete walls. I destroyed about 4 Hardpoints, and maybe some other things, I don't entirely remember, but I was still unable to build.

Thanx,
Icechisel