Metal spool to storage shed?

[RS3]

Acquired a metal spool that's 7 feet in diameter and considering making it into a storage shed. Thought I'd start with a rectangular base out of 2x8's or 10's to set the circles in and a few braces to keep it square. By doubling the short side of the rectangle(inside and outside of the spool) I could put in a floor.

I plan to skin the ends with plywood but I'm having trouble figuring out what to skin the rounded part with to keep rain out of it. Any ideas would be appreciated. I really want to stay away from using a tarp for aesthetic reasons, aka, if momma ain't happy....

[PBFrijoles]

What about tin amigo?

[Texastaxi]

Sounds like when you're done, you'll have a framed up shed, with a metal spool inside it.
Or I'm not understanding your explanation.