I’m not sure if I can actually help you, but it could be very beneficial if you elaborate on “doesn’t build anymore”.
I don’t think anyone will be able to diagnose the problem without knowing any of the symptoms.
I had the same problem building a DLL using MonoDevelop when including the UnityEngine.dll in the project - the program stopped outputting a .dll file right after unity was included. I found that using the latest official version of MonoDevelop + the latest GTK# package from Redirecting… worked just fine!
So just a heads up to others trying to do this (especially useful when your on a mac)