Thanks Joe, Appreciate it. Just the info I need. I was more or less interesting in common practices. Got the first beam up (its a shed typre roof) and jumped up and down on it while tied in to a tree( for safety) and the 8x12 held up without much flexing actually. The actual span was only about 14 feet 6 inchs > I found several formulas but cun't maske head nor tails of them lol. If my 200 lb self can jump on it without much deflection I think it'll hold. Sorry to post such a specific item to the forum