Rust building grid?

Hello Rust community!

I’m currently making a city with the purpose of acting as a giant battle arena, but I’ve encountered a problem…
I’m wondering why can’t I place anything inside theese walls(see link)?.. Driving me nuts… and ruins my arena… :confused:

http://www.worldwiderust.com/gallery/m/22995311/detail/194927#pid=1814709

you you have to build foundations from outside to the center. than build your house and remove the foundation around it.

I have tried that but that only works some places… the place I want to build is the area right in front of me in the pic. but I’m standing on foundation #3 from the wall and I can’t extend it any further from there…

[editline]8th May 2014[/editline]

http://worldwiderust.com/gallery/m/22995311/detail/194927#pid=1814725

I’ve taken a new picture, the foundations on the right side of the picture is where I took the other picture showing the open area. So as you can see I can’t just build from the outer walls since they are too elevated…