I own a machine I designed and a friend with better equipment built for me. I use it for my business. Cutting area is 850 mm x 345 mm x 135 mm (with current table set up can go deeper though). A good one can be built using steel box section. Mine is built using Aluminium extrusion and plate, not a cheap option but it allows for the repeatability and exactness that is need in my work and the ability to cut metals up to and including bronze. So it depends on what you want to do and how you want to use the machine.
Remember rigidity is your friend. MDF is not worth using even when resealed once cut to shape. it really depends on what you want out of the machine and your budget/time constrants. If you want some forums that I can recommend ask and as long as the Admins don't I will post (I am not an Admin nor moderator on any of these sites and get no cash benefit from them).
Michael
