Rebecca
This is how my husband made the table top for my free arm.
The measurments are 18X24 inches. He used 1/2 inch thick Oak plywood finished on both sides ( you can use any type of plywood)
He tracedout the measurments to fit around my machine on paper first then on the board.
The legs are from 1 inch wooden dowels cut to height minus
he screwed on adj. feet he found in the hardware dept.
The top fits even with my machine, and is easy to remove. I covered it with contact paper to give it some class.
Nancy Notions catolog ( which you can find on line at www.nancysnotion.com ) has it shown in plexiglass.
Good luck. it makes it so much nicer, especially when sewing smaller pieces, it's not droping off the ends of the machine. If you have any other questions, please PM me at home
Barb