This will be the first in a series of posts that step through the construction of my MAME cabinet, written after it was completed, serving hopefully as a guide to anyone who wants to build their own. Particularly those who have a level of handyman skill like mine: able to work a saw, but no expert on carpentry techniques.
Your first step is to design a cabinet. Most of the designs I've seen online, though very, very helpful, get things backwards on one point. They all assume that your monitor will be whatever they consider the default, and predicate the entire construction around that; so if you end up with any other monitor, you will have to adjust things and end up with something that doesn't look that great. I think you should figure out what monitor you want, then adjust your design around that.
Most of the plans I've seen online assume you're going to use a 27" CRT. Maybe if your coin-op heyday was in the 90s that size will seem appropriate, but to me, that seems way too big. The games I want to emulate had screens closer to 17" to 20". And nowadays, you can get a very nice HD monitor that will give you some beautiful displays in a size close to that, and for not that much money, so you'll have an ideal size to emulate 80s games. I think playing Burger Time on a 27" monitor would make me worse at it since I couldn't see enough of the screen at once!
So my first piece of advice is to choose and purchase the monitor you want first, then design the case around that, and your controller. My cabinet uses a Vizio 22” 720p LCD HDTV which I got for $165 on Woot.com; in addition to being a great size, having lots of inputs, and a great price, it has a nice black case that fits in wonderfully with my MAME system plans. Anything along those lines should do nicely and probably can be had for a great price.
Once you know the monitor's dimensions, you can figure out everything else accordingly. The monitor's width sets the case's width (plus 1½" for the sides themselves). Using a flat-screen means the case's depth at the top is limited primarily by the depth of the marquee (with room for a fluorescent light and a vent fan); the depth at the bottom is limited by the size of the controller board. My case ended up 23½" wide and 24" deep (the control board hangs off the sides considerably, of course).
Actually making the design is best done on a piece of paper, or suitable software if you have it, by starting at the bottom front. Draw a line up for the front bottom, up to the height you want your controller board to sit at (about 32" worked for me). Then figure out the angle you want the controller board to sit at, and using its measurements and some trigonometry, draw the lines for its bottom and back. (If you're building your own controller board, this should still be the same, because you should probably still build that board separately, so it can be easily removed for repairs or replacement.) Then draw another line for the height of your monitor, tilted back at the angle you want it. Continue up from there with panels for the speakers (and a bevel plate between the monitor and speaker plate if desired) and the marquee, and you'll find yourself finally at the top front. Now draw the top and back, and you have the profile. Everything else follows from that, plus the width.
That's why there's no single standard for plans. You need to start with the sizes of your monitor and control board, your preference for the height and angle of the control board, and then everything falls into place from there. Using my plans as a starting point will only help if you adjust accordingly.