Looks good!!!! I just realized how old this post is though...LOL....
IF...you still check it, try to move the heater, so you've got that bend out of it.
Straight shot up and out is the best....also, it looks like the flue goes out relatively low on the roof, I've heard that it's best to have the flue exit the roof at the highest point, that way, if a steady breeze comes along, it wont effect your draft.
Something like the air gets turbulent blowing over the pitch of the roof, and makes sort of a "dead spot" If it's down lower on the roof line.....(friend does hvac)
Also, when I get mine installed.....I'm going to pipe the combustion air in from outside, that way the stove's not using air from the room....which, if it starts burning real good, creates a "vaccum" inside the garage, essentially pulling in cold outside air thru the cracks in the building. It'll have all the air it wants from outside, keeping the warm air inside...Plus, you're not burning your breathing o2 as well...
Did you wind up making the burner from pots and pans??? How's that working for you??