Okay, this is a quick test image. A positive and negative cylinder for walls. The group declared positive. A positive cylinder and cube set so they create an arch in intersection. Grouped and the group declared negative. The group made bigger along the Z axis, so it goes through the both sides of the walls. Set where you think it would be appropriate for a row of arches to be. Duplicated, the duplicates rotated around the Y axis, to proper places. One of them duplicated again, made bigger and lowered to the ground, where a door would be, the Z axis shortened so the group goes through just one door. Everything grouped. the group declaared positive. Copied (ctrl-C) the inner, negative cylinder. Pasted with ctrl-V. The copy declared positive, the Y dimension made way smaller, as appropriate for the height of a row of seats. The positive seats' cyl duplicated, made smaller on X and Z, bigger on Y axis, made negative. Grouped with the positive seats. Everything duplicated for the second tier of seats, the negative cyl made wider. That group raised to its position, grouped with the first tier of seats, the group made positive. The door copied (ctrl-C), pasted and grouped with the seats. The group declared positive, for possible future work. Everything grouped together so it can be moved. So there's what you see. I used different textures, so it's, hopefully, more visible. I hope you can use the technique for what you want.

-- erlik