Is it normal for flat roof panels to come out rough on the AD5X?

Flat roof panels are usually a top surface quality issue, and the stock AD5X profile tends to print top layers pretty fast. The ridges you're seeing are almost certainly the lines between extrusions showing through. Two things help: bump up top wall loops so the top layers are printed as continuous lines rather than infill, and slow the top surface speed down. Also check your flow ratio. Slight over-extrusion makes each pass bulge and push into the next one, which reads as ridges on big flat areas. I dropped flow to around 0.95 on my machine and big flat tops got noticeably smoother.

The stringy underside on the overhangs is a diffrent animal. If the roof has sections that slope out past thier support angle, the printer is bridging or overhanging in mid air. Enabling supports for those parts, or adding a small chamfer to the model so it steps up gradually, cleans that right up. If the overhang is shallow, turning on the bridging settings or just lowering the speed for overhangs helps the plastic stretch across instead of drooping.

On the loose fit, that's usually two things combined. Most multi-part models are designed with a small tolerance gap so parts don't fuse together, and then dimensional accuracy adds or subtracts from that. If your walls came out clean, your printer is probaly fine. Check if the model files list a tolerance setting or if the slicer has an XY compensation or hole/contour compensation setting. Some models are designed expecting a small negative offset to tighten everthing up. Glue and filler is honestly a normal part of the hobby for big assemblies, so don't feel like you did something wrong, but a touch of sanding on the mating faces plus testing one small joint first would save you some frustration next time.

For the ridges on big flat tops, honestly a light sanding pass fixed more for me than any setting change did. I printed a clock case last year with big flat panels and chased the same thing in the slicer for weeks, then finally just hit it with fine grit sandpaper and a filler primer coat. Looked way better in twenty minutes than it ever did straight off the plate. Since yours is a shed model that gets looked at from a distance, that might be the easier road than chasing a perfect top layer. For the gaps, I've started dry fitting everything before any glue, that way I know which joints need filler before it's permanent.

Seconding the sanding and filler primer route. I did a big flat-topped planter box last fall and wasted a couple weekends messing with settings before giving up and just sanding the top down with fine grit, then two light coats of filler primer. The primer really hides those lines once it builds up a bit. One extra tip, do the primer in thin coats rather than one heavy one, or it can sag on the edges of a flat panel. Also on the loose joints, I found roughing up the mating faces with sandpaper before gluing made the glue grab way better on mine, the smooth surfaces were almost sliding apart untill I did that.

Still figuring this forum out so sorry if this is a dumb question, but on the loose fit thing I had something similar with a birdhouse I printed last month. What helped me was printing one joint section again with a tiny bit of scaling on just that part, like 100.5 percent, and it snapped in way tighter. Not sure if that works on the AD5X slicer the same way though? Also curious if anyone thinks old filament could cause the stringiness, becuase mine had been sitting open in the garage for months and I wonder now if that made it worse.

One thing I'd add on those roof panels, try printing them tilted back on the plate instead of flat. I did a lighthouse model last summer with a couple of wide flat sections and propped them at about 45 degrees in the slicer. The ridges basically vanished because the layer lines stack differently and the underside comes off supports in a cleaner way. Costs you a few supports but way less than sanding the whole thing down. Also worth checking how old that PLA spool is, damp filament gave me stringy overhangs for a month before I figured out what it was.

So I tried the scaling thing for the loose joints. I re-printed one of the wall sections with just a tiny bit of extra size applied to it. It was a simple fix but it made the pieces fit together way better than before. relly appreciate the pointer on that.