I hate it when I go to a job site and see some carpenter trying to cut a long molding while his $800 miter saw is balanced on a piece of drywall set on a plastic trash can. For one thing it's dangerous. I like a continuous wooden table that's long enough for me to safely trim the end of a 10-footer. I also want to be able to screw a stop to it for repeat cuts.
This is the saw stand I use. It takes me two hours to build; it's made of four 8-foot 2x4s, an 8-foot 2x6, less than half a sheet of 3/4-inch plywood, a few 1-5/8- and 3-inch drywall screws, and four 3-1/2-inch-by-3/8-inch carriage bolts. I usually mount a power strip on it so I can use it as a workstation too.
You can figure it out from the pictures, but here are a few tips. The 2x6 crosspieces that support the work surface are notched to fit between the 2x4 rails so that the infeed and outfeed tables are exactly the height of the chop-saw table (the table on one of my saws is 3-1/2 inches high, the other 4-5/16 inches high).
The center platform is about an inch longer and wider than the base of the saw. I usually use 48-inch-by-12-inch pieces of plywood for the upper tables. You'll probably have to cut the corner off the right-hand table to clear the handle of saws that miter to 60 degrees.
I usually don't add fences to the wooden tables. The saw's metal fence works well enough even for long pieces, and I can easily screw on a zero-clearance table and fence for cutting little fragile moldings.
Jed Dixon is a stairbuilder in Foster, R.I., and a presenter at JLC Live. This article first appeared in The Journal of Light Construction.