Exercise - Angular perspective

In this sketch, of an imagined hut, I am trying to get to grips with two point perspective. Think I made up my own  rules when it came to adding the roof, that said I think it is in keeping with the rest of the  hut. 

Having an understanding of these rules of perspective when drawing pictures where you want to add both a sense of volume and depth is important...brings more realism to the composition.  

Will reluctantly keep the ruler close to hand...