You might take
some inspiration from this. Its actually bigger than your target size.
Basically, set four posts in the ground, attach walls with a gap at the top for ventilation, roof it. The biggest problem is the 6' max height (peak of roof, I assume?) - that means you can't build a walk in, which (honestly) sucks. But an 8x8 structure is 64 sq ft of footprint, and involves almost no cutting, since you can buy lumber in 8' lengths. Plywood/hardieboard too. Or even Polycarbonate panels.
What you do want is either a 10' roof panel, or do some cutting so you have an overhang - say 8' wide, 6' deep, and use a shed style single slope roof, rather than what I did. That will give maximum height at the front, for your convenience when you have to work in there. Put the back (low) wall facing into the direction of your prevailing winter winds.