I'm not sure which you mean to be the 'front' side -- the one with the big doors? A very short shed-roof, sloping gently out from the top of the doorframe, would be easiest. If you get zero snow you might go as long as 12', but with meaningful snowfall it'd have to be shorter and/or exceptionally strongly braced. If you want a longer roof than that, it may be a little trickier than in most situations; you might almost have to make it follow the gable shape of the shed roof, which would be a pain in the butt (although doable).
Basically though the general plan is that you frame out a structure as if you were building a shed, add additional diagonal bracing (do not skip this step), then put on a bunch of parallel 1x or 2x lumber strips about 2' apart (depending on engineering requirements for what you're doing) to screw the roof panels onto. Whatever roofing material you're going to use, GET THE MANUFACTURER'S INSTRUCTION PAMPHLET THAT GOES WITH IT (may be available at the store, or you may have to download it online). I see *so* many people mis-installing roofing sheets, with them turned the wrong direction or massively unsupported or screwed on wrong or so much overhang the wind will rip them right off. Find out how you are meant to do it, if you want the roof to last.
Good luck, have fun,
Pat