I put a wood stove in my quonset garage and wished I had saw the similar building on display at a state fair that had one first..
I cut a hole in the side of the building for the stove pipe (actually two,one right above the other,as I had found a used hot air oil furnace that needed to be vented)---I cut the wall arch just below a seam where two panels overlapped,that allowed me to shove a piece if sheet metal in between the panels and bend it outward,to make a deflector for rain water...
I learned the better ways to do it were to not cut the hole on the flat side of the arch,if I had cut the angled "sides" instead I'd have had a lot less water,as rain flows right down the center flat section of the arch like a river--but overall,the amount of water that actually gets in is not much...and a good hi-temp RTV would seal around the stove pipe if I were that concerned about it..
The building at the fair like mine simply had stove pipe running straight up all the way to near the peak,and they cut the angled part of the arch to pass thru it...this provided a lot more heat,coming off the length of stove pipe..my method of running the pipe out the side of the building with only one 90 degree elbow and maybe 2 feet of pipe before it exits doesn't allow for you to get any real heat off the pipe itself,which is often as much or more than the stove throws off..
I'd look into all the local codes and insurance regs too..my install is probably "illegal",but when I put the building up in 1992 the building inspector only asked if I had a permit for a wood stove,and I said "yes--but for the two in the house,not for the garage"..he said that was no problem,that covered it (then,maybe not now!).
He said to "put the stove up high as possible,that way vapors from any leaking fuel wouldn't be as likely to get sucked into the stove and possibly flash and start a fire..my barrel stove has always just sat on its legs right on the slab,its only about a foot off the slab..I never had a problem,but I don't leave anything leaking fuel in the garage to begin with..and boot out anything that does if I plan on using the stove..