Don't use PVC. I have personally been in a shop when a 3/4 or 1" line let go up in the rafters for no reason. Nobody hurt but we thought something had gone horribly wrong with the oxy/acteylene we were using. I would not have want to been near the shards it let go, though.
My shop when I bought it had pvc, it was the first thing I replaced to black pipe. Money well spent.
I'm for the tie downs in the floor, if you can make a decent cover for them. I used to work in a shop that had them, one tie arm was broken, the other ones the lids were constantly getting tilted off, and you would drop a forklift wheel in them, or the caster on a toolbox or rolling cart, and they were a pain much more than we ever used them.
That same shop had a center section that had a sloped floor to a drain, that was covered with a pipe welded together grate. It was kind of nice if you pulled in something covered with snow, it could melt off and run all in the drain. But any time you would drop any tool, or a special bolt or fitting, etc. You know exactly where it rolled- right in between the grates. And the sloped floor was a pain to weld up anything big, it was tough to build it because the floor wasn't flat- So I wouldn't recommend a sloped to center drain floor.
I have debated a overhead or jib, but I really don't have room. Plus I have a roll around gantry/a frame and forklifts so that kind of eliminates the need, and the post and arm type seem to never be in the right place, or they won't quite reach where I want to work.
I have a big apron out in front of my shop, and its really nice.
Big doors, tall and wide.
Plenty of benches, even though I have probably 50' of bench space in my shop, I still work in a 4'x 2' spot, I still like having a lot of bench space.
I like having a separate room with shelves for manual's, filters,small spare parts, etc, that is separate from the main shop.
My shop doesn't have eave troughs, which is nice, because its got trees down one side, so I don't have to clean them out. But I did spring for a 8' piece of gutter right above the walk door, so when I have to stand in the rain fumbling with my keys, now I don't get wet.
I like the pictures I've seen of the big bifold doors for ag machine sheds, and I think it would be nice to have a apron, that the open door created a shade for.