I am a big fan of Team Fortress 2, so when I experienced the build system in Project Reality, I thought it could take some ideas. In TF2, the class called the Engineer can build a variety of machines. When building the machine, a 3D blueprint of the object appears in front of the player, allowing him to move around to set it, and rotate it 90 degrees with the right mouse button. This system ensures that you will know exactly where it will be built, and allows for building it exactly where you want it.
I'm sure most of you have expererienced the frustrations of building things as a squad leader in Project reality, I know I have, so being able to know where something is going to be built, rather that building blindly, would be a great change.
Also It would be nice if barbed wire could be built on a slope, rather than leaving a big space underneath for people to cross under.

Finally, I suggest adding a destroy/demolish command to the squad leaders commo rose, so if he or she dosen't like where something has landed, wants to move it, or it didn't come out just right, they can rebuild it without having to spend all their ammo or anti-tank rockets destroying it.