How much access & elbow room you need on exterior side, merely claustrophobia inducing or true crazy-making tight?
Before I put up a $200 Sams Club 10x20 tarp enclosed shed/shelter just over lawn I toyed with the idea of 'Pony Walls" or mounting the preformed cheapo tube frame bases on a 28, 32 or 36 inch tall plywood and 2x4 foundation and have it cover everything from the entrance door back...Note, prices have gone up since! We ended up getting seven years out of the utility shed.
<--- They sent replacement roof a month out of warranty no questions asked... Their 2-inch leg kit held up in snow and storms okay with decent cable tie downs out from edges of roof frame. I'm not seeing it but they had tensioned steel aircraft cables to keep roof trusses from spreading under snow load.
The factory store is full list prices unless one catches a special, $300-ish for a mouse-magnet... err... perfect weather deflector over a vintage AS seems easier than reinventing the wheel - remember PVC tarps need to be heat welded or sewn with thread, there is no adhesive to hem up custom awnings etc..