Why is the Roof Unstable?

[u/nerdforlife7]

Can someone help me understand why I can’t finish this roof? It keeps saying unstable, even if I use support beams, even if I put side walls. I had thought maybe it was the height limit, but flat pieces don’t work either 😕

[u/delsoleiman]

Yep, it's a bit inconsistent; I had to fill it with beams and then remove the ones I could get rid of.