I personally prefer steel roof for the longevity of it. I do not use shingles anymore as hailstorms seem to be becoming more regular around here.
With wood storage you have to deal with some tradeoffs with most all set ups and I'll pass along what I've found. We store ours for quite a few years sometimes so maybe this won't apply to all. If you're going into a wood framed building, think about powder post beetles and termites. We normally spray every once in a while but still see some damage from them in wood posted buildings. In some of the barns we store in we are on dirt floors. What, if any, rots up is not much. The main thing there is to have good drainage around the building. If you have no gutters, run a perimeter tile around the building and try to get the floor level a little higher.
For air circulation we leave the bottom edge a little high so air can circulate through. The problem with this is animals. Coons, groundhogs and opossums love to get in there and dig under or poop on top of the piles. We combat with traps and such but it's a hassle.
You can see how the lower edge is open here on this barn.
This shed is probably the easiest to load and unload into. Back the truck in and go to it. Once the lower part is done you can stand in the truck bed to do the higher stuff. Again, long term storage for us and we want as much as possible in there out of the weather. Less labor not to stack but we value the space.
We have a couple of grain bins too that we used because they were there. Royal pain and I HATE stacking them up. Done it a few times with these and would put them on the bottom of the list. These have walk in doors and we stack as high as possible. Then we back the truck up and one guy throws in and the other stacks it to the angled roof as shown below. Takes more time than it's worth to me but beats nothing.... by a small margin.
When I set up my building that houses my boiler and years supply of wood I went with concrete block sidewalls and concrete floor. Even went so far to put rebar in the blocks cores and fill with concrete. No ricking needed, no bug problems and easy to clean.
Another thing I'll mention too if your looking for more than a years storage. Put doors on both sides of the building if possible. That way you can fill on one side and take the driest from the other, keeping a constant cycle going. If you use it all in one year not needed but do that with some of ours and makes it nice.
Again, I'd put my $ into drainage tile and gutters before laying stone and such.