Black Sheep I've got one of those metal sheds.
As GB says.....Gloves are a must. Other things learnt the hard way.......
My doors slide open inside the front panels, so when it rains water runs down the doors, which are on the inside of the threshold, into the open ended door bottom guide channel. There is nowhere for this water to go except into the concrete floor. Masterpiece of crap design!
In winter, it suffered from shower style condensation on the underside of the roof. Research showed this was moisture coming through the floor. Mine's just on slabs. Cured with a membrane, topped with a strandboard floor. Hope you put a membrane in your floor structure. Otherwise its a membrane and another concrete skim onto the existing floor.
Overlap the roof panels so the overlaps face away from the prevailing wind, regardless of the instructions, and put a bead of flexible mastic on the roof panel joins as you go. Rectification is awkward as the roof won't hold you without additional elaborate support. Even after light rain I ended up with drips from the joins on some of the roof panels. It was quicker to strip the roof than struggle. A fillet of mastic cured it, but I never saw anywhere that water could get in, so a mystery.
I also sealed the roof panel ridge joins, using a horrid greasy mastic waterproofing tape of yesteryear called Sylglas that worked a treat but I left a vent hole on each of the raised ribs. These are covered by the ridge capping.
Otherwise, like me, you'll wonder how you managed without it. Crude and simple, great for storage, but not as homely as a wooden shed.
Swarfy.