Here's my guitar shape palettes. I made these from 1/4" birch plywood that finished on both sides. The plywood looks nice, is stronger and less likely to split than solid wood. The only finish is a little linseed oil rubbed into all sides and left about a day to dry. When I'm fished painting for the day I just wipe off (and rub in) any excess paint with a rag or paper towel. After a while they develop a nice neutral patina.
The first one I did is about 18 x 24 and was based on a fender srat body. I simply sketched it out first, and then cut it out of a 2'x4'plywood sheet using a jig saw. The second picture is a detail of the back showing a piece of metal I epoxied on that fits into my hand when holding the palette, an innovation that makes it more comfortable and secure to hold. It works very well.
That first palette was a little too big for the way I normally paint, and I had some plywood left, so I tried making another one that was a little smaller. This one is well used and has a nice grey patina that helps judging colors. It gets quite glossy and smooth too.
The newest one I made is much smaller and shaped like a les paul. As you can see the "neck" area is a great place to keep the sulvent cups. The smaller size allows me to get up close to my work and is quickly becoming my favorite palette, just as the real Les Paul has become my favorite guitar.
These can be fairly easily made yourself I less than an hour.
If you would like one that hand made by me, I can make them at $18 for the small (approx. 8"x11"), $25 for the mid-sized (aprox.16"x20") and $32 for the large (approx. 18"x24"), shipping will be extra. Each one will be hand made and unique and made to order. I can also customise one to any guitar you want including accoutics. For an additional fee, I can also make them in animal or other object shapes. They can also be made of any solid wood of your choosing. The cost will be based on the diffcaulty of the shape and expense of the wood. Email me at email@example.com if your interested.