Trimming: Ideas on Wraping and Casing the Skylights

How you trim out the skylight depends largely on how the drywall was finished. If you finished the corners with corner bead, you don't have to do anything else. You might want to put some wood up near the skylight, if the drywall wasn't as tight a fit as you'd like. I'll quickly walk you through that, then we'll continue with other options.

Wrapping The Skylight

Measure the perimeter of the shaft at the top of the skylight. Add about 2' and then get some 1x4" wood to match your existing trim. Select the best face and edge. Use a router to cut a 1/8" roundover on the corner that joins the face and edge you selected. The edge can not have any defects in it, as you will be staring right up into it. Sand the wood with 150-grit paper and stain/finish to taste (I don't mean for you to taste the wood). Skylights Trimming
If your shaft is straight up and down, it will be easy to cut the wood. Just measure one of the long sides, cut the wood to length and nail it to the wall placing the 'ugly' edge up agains the skylight. Be sure you locate your studs first, and use 2" finish nails.
You want to create a wrapped look, so the next part is a bit tricky. Note the end you cut, that is where the next piece will go. You want the wood grain to continue all around the opening. Measure for the next piece and nail it up. Continue around the shaft in the same manner.

Casing The Skylight

For those that installed plywood, or didn't apply corner bead to the bottom, you will want to finish the bottom of the shaft with wood. You are basically going to do a 'picture frame' type casing, like you would for a window. In addition, if you used plywood on the shaft walls, you'll want to wrap the bottom perimeter in just the same manner as the top. That way you can cover the plywood edge with your casing and use the solid wood for a reveal. This will, of course, leave a little tiny shelf for dust to collect on, but I doubt anyone will notice, since they won't be able to see it.
That about sums it up. It's a great project which I highly recommend. It's not only fun to do, but makes any room seem more open. There are several models of skylights available, even those with a remotely controlled shade to block the sun when it isn't wanted.