The easiest way is just to do a google search, since there are a number of plans (and design concepts) on the net.
One of the simplest designs uses an MDF framework, with black iron gas pipe and rollerblade skate bearings as linear rails and bearings. Plans for this style are published by a man named John Kleinbauer (AKA Cranky) on his site,
http://www.crankorgan.com. Sadly, his construction forum was recently made private, so you can't just go there and get ideas, anymore.
Many people on this forum have built his machines, or something heavily inspired by his machines. (CNC Parrot is someone who built a machine by looking at pictures on the net, and "parroting" or copying what he saw)
There are also many other people who have published designs for CNC wood routers, but Cranky's seem to focus on home woodworking, and just making something that works from parts largely available at Home Depot.
For increased accuracy you will want to use more rigid construction, and higher precision parts -- there is something called a ballscrew and ballnut which is a super-precision screw drive. The nut is actually a helical ball bearing that threads onto the special screw thread. Very cool, extremely precise, and hideously expensive for a homebuilder.
Just hang around this forum for a week or two -- I went from complete novice to stripping down printers for their stepper motors, in just about a week. I'm gathering up parts to build my first machine, right now...just got the iron pipe for my rails, Saturday, from Home Depot's scrap bin. I love free stuff!
A machine for woodcutting is relatively simple to build -- milling needs more precision, and consequently more rigidity, more cost, etc. And, it's a significantly different task to build a machine with an active table 5 inches square, than it is to build one to accept 4x8 foot sheet goods.
So, what do you want to build? Or, more precisely, what do you want to do with it?
-- Chuck Knight