How did you do the roof? *8' on front and 7' are rear or similar?
Should I skin it with corrugated metal? *That seems the simpliest,
though I don't know about cost compared to osb and a paint job.

Any books or websites to study?

I did a slightly peaked roof with the ridge about 4' from the front, I
used 2X6 rafters, then 2x4s perpendicular on 2' centers to screw the
roofing into.
Id have to measure the height, but the open side is tall enough to let
my backhoe hood slip under including the exhaust. That helps when
cleaning & setting round bales of bedding.
I wish I'd used R panel for the roof, but the corrugated is adequate
and cheaper, however, every time you walk on it you have to go inside
with a broom handle and knock the dents out.
I just don't like or trust OSB, and paint and animals don't mix, if
you paint the inside expect to do it annually. they rub on the walls,
they throw bedding, and unless the are better behaved than mine, they
poop everywhere.