Im quite sure that there is a way to get that problem fixed somehow (with an elaborated support beam structure) but building with normal wood only works up to a certain height (not an expert here but i would say 4-6 meters (2-3 vertical 2 meter poles) high and then you start having trouble with any roof you want to attach to the building (unless you know how to/figure out the support structure if any is possible). You should go into the Black Forest and get some Corewood - that will allow you to build higher structures (there are 4 meter Corewoodd poles/beams) that will also have a much better ceiling height when compared to normal wood (IMHO).
PS: Roof stability also depends on how wide the building is between the roof supporting walls/elements. But that does not seem the problem with your building (at least not the primary one causing the collapse).
PPS: I could not see that on the video but using pillars or poles in order to build a platform or foundation on which you then build the building effectively takes away one "stability level" - this also applies to "partial foundations areas".