The dimensions of my cab are 20.75" wide / 24" deep / 62.75" tall.
I used 3/4" plywood, so the inside dimensions would allow for a 19 inch monitor, but only an LCD would fit. Plus I felt the hole in my pocket book after I bought the 17" LCD, especially seeing as how it would only be used in a MAME cabinet... If I would have made it about 30" deeper, I could have used a regular CRT monitor and been several hundred dollars richer.
I didn't want to use a TV or arcade monitor due to some of my games are "vector" games, plus they wouldn't have fit in the cabinet and I already had a CRT monitor (at that time anyway...). The LCD monitor works pretty good. I used some scan lines on the regular games and none on the vector games.