A guy I know had one of those similar to this given to him,after the tarp cover shredded badly after 10 years...owner decided it was time for a "real" permanent taxable garage....
The guy used the steel metal from a old swimming pool to cover the arches,he saw some pools on craigslist for free so he went and dissassembled them carefully so as not to muckle up the metal,he rolled it up like carpet ,and duct taped it so it couldn't unroll,to get it in his pickup and home...there is at least one "free pool" ad here daily on craigslist,a lot of new home buyers simply want them gone!..or ones that no longer have kids or can use & maintain them want to be rid of it..
His arches were round like pipes,he used 2" conduit "U" clamps to attach 2x4's across the outside of the arches for purlins,and put the metal from the pool on them, with those self drilling screws with the rubber washer heads on them...it survived last winters 8+ feet of snow and several 60 mph storms !..he made wooden endwalls out of 2x4's and OSB boards from pallets he also found for free on craigslist..
I just score about 60 feet of old swimming pool steel myself about a month ago,and wish I could get more of it..--all epoxy coated.it'll never rust,its 11 years old and still looks new--I hope to be able to put it over the plywood end walls on my quonset garage,that are starting to rot a bit at the bottoms and always have paint peeling off them --it'll be permanent metal siding that will outlive me probably..
I got lucky and found a person who had the pool taken down and was fairly careful about rolling it up,then the person he hired decided only the non ferrous metal was work scrapping--he never came back for the steel..I do not think I'd want the job of taking one apart,especially in summer heat,I doubt I could do it...