if you have a metal roof supplier in your area, call and ask what the price is on galvalume. They will cut it the length you need, and can supply all you need to install it with, screws any trim you might want, etc....
something else, you can ask if they have any seconds and also if you tell them you don't have to have the warranty, you can get it cheaper.
Not sure where the idea that metal and shingles is about the same cost, if you figure the whole roof cost, 1x4 perlins instead of decking, no tar paper and installation time, metal roofing is by far the least expensive way to go. I was over at our local metal place today and was talking to the guy there about a few pieces I need for a project, and he said what they sell has a 40 year warranty, Not sure how expensive 40 year shingles would be, just sayin
ok, I had to go do some math to make sure I knew what I was talking about. breaking it down like this, the metal panels come 3 ft wide, so to do even amounts of both I'm figuring 300 square feet.
Galvalume, which is just plain unpainted galvanized metal roofing, in my area, is $1.49 per linear foot, obviously a 10 ft piece would be 14.90 each. That's 30 square feet, so 10 of those would be $149
limited lifetime shingles are 24.50 a bundle, and it takes 3 bundles per 100 square feet, that works out to $220.
This is just the roof covering itself, add in for shingles you have to have decking and tar paper, and that shoots the price up even more. For a chicken coop/shed, no decking or tar paper is required, don't use pressure treated boards for the perlins and you're good to go.
Said all that to say this, in answer to the original question, the cheaper of the two would be the metal roofing.
Rolled roofing is 42.50 per hundred square feet, so 3 of those would be $127.50, but you still have to do complete decking and underlayment. 30 lb felt is $15 dollars a roll, 200 square feet, so you'll have to buy two rolls, so now that's close to the metal roofing, and depending on what you use for perlins, you're looking at almost the same cost. The rolled roofing description didn't give a warranty period, so there's that too......
I'm just sold on metal all the way, cheaper, easier to install, lasts as long or longer and my opinion looks better