I built mine on the fly with a few rough sketches. This was the result of having an accumulation of parts and material from 'here-and-there' and a determination to make the design fit the parts. The compromises are many but it works okay(ish) . Here's a pic fwiw. See what happens when you don't use a map ?
4x8 means the goal is plywood or other soft sheet goods ? If so the design parameters become clear. You won't need much clearance or travel on the Z axis but the long Y span will need the to be stiff.
Honestly I'd probably buy a kit like cncrouterparts and let them do all the cutting and measuring.And what one would you use today?
Anyway the real reason for replying was to share this link:
CNC Router Source: The Ultimate Information Resource
It's not a plan but it's a guide of sorts and gives a lot to chew on.