Furnished content.
(from Lumberjocks.com)
I built a lattice fence to put around a hot tub, and wanted to put post caps on the 5 posts. I went shopping and the ones I saw did not look like they would look nice for very long. The corners were mitered, which I thought would eventually split apart. The pieces were stapled, and again just didn't look very well put together. And they were expensive…over $20 each. So I decided to build my own using solid wood…no mitered corners. And here's how I did it….I bought a rough sawn 2×8x8' (1.75×7.75×96 actual) cedar board at a big box store. I was lucky to find one with no knots. I cut it in half and planed one board to 1 and 5/8 and the other to 1 and 3/8. I then cut the thicker board into 6 pieces that were 6.75×6.75…these will be the bottoms. I cut the thinner boards into 6 pieces that were 7.25×7.25….these will be the tops. I only needed 5 pieces of each, but the extras ones were for practice. My fence posts are 4×4 treated posts with 3/4 thick cedar board cladding, which made the posts 5×5 (actual). If your posts are 6×6 (actual 5.5×5.5), you'll need to make your squares wider.
Next I took the tops and routered at 3/16th depth to create a square on the top. You could also use a table saw to cut all the way around, just leaving the square. The square is 4”x4”.
To create the slope I used my table saw set at an angle. I can't remember the angle, but I wanted to leave the edge at 9/16” high. I then used my router to create the hole that will sit over the post. I made it 7/8” deep and 5.25” x 5.25” square so it wouldn't be too tight on the 5×5 post.
Next I routered the top using a 3/8” round over, and I routered the bottom using a yonico #16135 molding bit.https://www.amazon.com/Yonico-16135-Architectural-Molding-Router/dp/B00KZM2J6Q/ref=sr_1_2?crid=10WZ6L033ZI24&keywords=yonico%2B16135&qid=1650853683&sprefix=yonico%2B16135%2Caps%2C76&sr=8-2&th=1I didn't use the whole profile of this molding bit, so you'll have to use care to set it up correctly.
I then screwed the bottom to the top (from underneath) using stainless steel screws. 
I used Gorilla silicone sealant to attach the post caps to the post. I didn't use any mechanical fasteners, as I didn't think it was necessary. 