There are three things that need mentionimg here:
  1. Follow the directions exactly;
  2. Everything fits; do not use a hammer to pershuade anything, except ...
  3. When assembling the walls, use a block of wood and a rubber mallet to gently nudge each panel forward. I will explain.

As I was assembling this shed, I got a little too anxious to see what it would look like from the front, so after installing the first two roof panels, I broke from the rules and installed the front end roof (or ridge) cap between them. I ended up with the doors not fitting together vertically as they should, and I think that premature ridge cap may have been the reason.

Here is my belated logic: The directions guide you to work evenly from front to back: a roof panel on the left and a roof panel on the right, front to back until the rear panels nicely overlap the rear gable. Then you install the ridge caps, front to back until the final one overlaps the rear gable.

There are, or seem to be, roughly a thousand or so screws involved in this process and if you follow the directions, they too are being installed evenly, left and right, front to back. Think about it; every time you tighten a screw, it is exerting a degree of pull on the entire shed; not just the parts that you are assembling. That screw is pulling the entire shed very slightly north, south, east or west. Done in order, the screws on one roof panel will just about counteract the pull of the screws on the opposite panel.

When I got to the final rear roof panel, I could not make it fit over its corner wall and gable. I had to pull it into place with a pair of interlocked 4 foot bar clamps and then force it down into its truss channel with a rubber mallet and block of wood. I suspect that this was because the premature ridge cap up front had thrown everything to follow out of whack. It also locked in the front end into a fairly ridgid structure, canceling the inherant flexibility that might have given me more flexibility at the rear end.

Regarding the 2nd recommendation above, I had also screwed up the vertical door alignment. When I assembled the right hand door, I had trouble sliding the steel channel over the hard plastic edge. Some WD-40 might have solved this problem, but instead I used my trusty rubber mallet to force it along the plastic grooves. Of course, that would have warped the steel channel to some degree.

Wouldn't it be nice if I could deduce these scenarios before the fact rather then after?

However, the tech support guy surmised that it was already warped and sent me a new steel channel, free, which did in fact slip on very easily. He also said that they are designed with a slight warp to make the door contact its mate at the top and bottom just before the center latch engages.

As you will see in the pics near the bottom of this article, the doors are still slightly out of alignment probably because I had broken from the recommended procedure. Fortunately I had built the deck with a slight tilt towards the front for drainage, so if any rain does blow in through the top of the door, it will drain right out again. (I tested that with a pitcher of water. It worked.)

The final point I want to make is not in the directions, to my knowledge. After fitting a wall panel into its pair of floor slots, tap the exposed edge with a mallet and block of wood to make it seat itself as far forward as the slots will allow it to go.

I did not figure this out until I got to the final panel of my first wall. After loosening some of the existing screws, hitting the wall edge with the board and mallet, and clamping down gently on the outside with my interlocked 4 foot clamps, the panel was able to get enough of a grip in its hole pair to stay put as I proceeded with the adjacent corner wall. And yes I did place the supplied 1x4 below each hole first.