Hey Henry, don't feel so terrible about it. If it can't be done, so be it. Can't you group a lot of beams and give them one material? Or in roofed object variation leave out the materials for unimportant parts (such as the inside). The structure one worked quite well, as does the roofed one you sent me.
In the Roman fortress I made in XFrog, I made the pallisades and such as one object, and the buildings inside it as another. Same size, and I just put them on exactly the same spot and they work together. That might be an option... beams as one object, roof as the second, to be placed over eachother.
I hope you manage after all.
---Dune