unless you insulate the wooden shed, including a vapor barrier, the metal shed will absorb less heat.
the good thing about a wooden shed is that, if local code permits, you can DIY much of it and thus spend a good bit less. and then you can insulate a more traditional shingle roof [which you also DIY] so it ends up absorbing much less heat.
I would, however, strongly suggest that you have the concrete pad, attachments to it, and electrical professionally done -- DIY in those areas is more like a professional doing it for himself
grampa -- ya, I'd DIY the project -- submit plans and pull permit myself, too