Any shape timber can be used in a frame, below are some shots of timbers used in Jack Sobon's house:




And:



And the opposite side of the last post:



Also:



On the left you'll see a forked tree trunk, back to is Will Beemer of the guild, and at the end of the hall in the kitchen is Jack (with the straw hat on).

Jim Rogers




Whatever you do, have fun doing it!