E and I have made window and door casings for nearly every aperture in the living room. Most of them weren't too hard, but I put off finishing the last window due to the difficulty of working with it. Let's make no bones about it: there isn't an intentional right angle in the whole living room except for those that I made (and even then...). The walls are not merely out of square, they're also out of plumb or bowed. In some cases, we fixed this by replacing drywall sections. In others...well, just look:

See that nice black triangle? That's the horizontal slope of the wall at that point. This is after I made this one better. It used to be worse. Much worse.

Because of this, some challenging woodworking was required. I still wanted the sill front and back to be parallel, but the sill would fit without some adjustments.

This is the left side of the sill.

This is the right side of the sill.

In addition to trimming these pieces to be inequal, the right side of the casing and its rosette needed serious shimming:

This is a 7/16" shim. Is it a shim or a stand-off at this point?

After installing and tweaking, it didn't look half bad.

See that bow in the baseboard? Some cameras cause that. When they do, it's called spherical aberration. This, however, is just the shape of the wall.

I really like the rosettes.

This is the bottom of another casing in the room. The trim underneath is the same as the vertical and horizontal pieces. E mitered turnbacks onto all of them, but the turnbacks are narrower at the bottom than the top and the front piece is trapezoidal, wider at the top than the bottom. This is one heck of a compound miter and let's just say that we needed a calculator that did arc sine and arc tangents and we made a lot of scrap wood in the process.

This is the door in from the sun porch. There was no real door casing built into the wall frame. Initially, it was just construction grade 2x6 fir stained brown. I had to build a door casing that stands proud from the wall and then added the finish trim.

This is more or less what the room looks like these days. It serves as our bedroom since the existing bedroom will be torn off the house pretty soon. You can compare this with the first page to see the difference. The big old hunk of wood at the top of the image is a plywood case to cover up the support beam. We realized after we moved in that we'd probably wouldn't get around to sanding, priming, and painting the finish carpentry until the addition is finished. Essh.