R. Cordova- First of all I need to know if your mitre is electric or manual? It makes some difference as to how to proceed. Also, in a room with only four sides, there will be two sraight cuts, and two double copes. Are you familar with mitre coping? If not, e-mail me and I will help. I am a professional finish carpenter with twenty years experience. You do not not need an electric jigsaw to make the cope cut, but that is how it is donein the field when production time is a factor. A coping saw will do just fine. Let me know what equipment you have available, and I will go from there.