Open triangles in wall ends

[Ernest Williams]

Hi I hope that I am doing this right. I have been designing a garage with an apartment above it. The main garage will be an RV barn with the apartment above it. The height of the RV barn is 15 feet or 180 inches. when I try to place the roof on it the end walls have open triangles. I have attached the picture to this post. Any help with be appreciated.

Thanks.