There might be some drawings out there. I guess I'd start by sniffing around the AR groups on the web. I have drawings on hard copy and I have some Armalite engineering memos, but I gotta be honest: I'm too busy right now to dig that stuff out and scan it in.
There's nothing about the AR platform that's different than any other gas-operated semi-auto. You need to pick off "just enough" pressure for a required duration to cycle the action.
The port hole doesn't vary by caliber so much as it varies by pressure of the cartridge. 5.56 is higher pressure than some larger caliber cartridges. The size of the hole varies according to what the pressure is where you choose to pick off the gas to cycle the action. You need to consider the length of the barrel beyond the port - if your port hole is close to the muzzle, you'll need to make your port larger to get that action cycling faster before you lose all pressure. Conversely, if you're porting the barrel closer to the chamber, you might have a tiny little hole, and you're going to have pressure of a longer duration.
There's rifle length, mid-length, carbine length and pistol length gas tubes. In general, I'd try to have at least 4" of barrel between your port and the muzzle. That's just a generalization to make your life easier. If you really like being a pioneer (definition of a pioneer: Arrows in your back and your face in the mud), then locate the gas port where ever you want and try to make it work.
I can't tell you what size you should be using for a particular cartridge unless it's a .223/5.56. I can tell you where to start according to your gas port location, but it is probably better that you measure it directly yourself. You should assemble your upper (with the barrel, barrel extension, and D-ring or floating handguard nut) torqued down to final spec. Then you should lock the complete bolt into the extension.
Now, put your gas tube into the upper. Bottom it into the gas key. Pull it back out by, oh, 0.050 or so. You do NOT want the gas tube to bottom into the gas key when the bolt goes into battery - it will peen the gas tube shut and you'll have to a) replace it and b) cut down the gas tube to make some clearance.
Mark where your gas tube (whatever the length of your gas system) ends with .050" clearance off bottoming in the gas key. Dykem the barrel, mark where the end of the gas tube is. Don't get itchy with the drill bits just yet.
Now you need to look at the drawings for your gas block and figure out where the hole in the barrel needs to be - it might not be directly under the end of the gas tube. You might need to position your actual hole in the barrel forward of the end of the gas tube in some gas blocks in some adjustable gas blocks.
Put the barrel into a vise with soft jaws (if you have a clamp-on gas block) or a super-spacer (if you need to put dimples on the bottom of the barrel for set screws), and then figure out how to get the gas port hole indexed to be vertical - you should determine what is "straight up" from the alignment pin that goes into the barrel extension (and into the barrel threads). That should be your indication of what the "top" of the barrel is. Run out to where your gas port needs to be and position the hole so that you can make your gas block work with your gas tube position and the hole position in the barrel. I can't tell you how to do this without seeing a drawing for your gas block. I make my own gas blocks from 1.5" aluminum round stock, which allows me to choose more barrel diameters than what are "standard."
OK, so let's assume you know exactly where your port is going and you've figured out the dimensions of your gas block. You do the usual stuff to make sure you're about to sink the hole into the top center of the round stock that is your barrel, center drill, then use a small drill bit to set up the first hole. Then run in a chucking reamer to enlarge the hole by no more than .005. This gets rid of your burr in the bore. Put on your gas system and go test fire your AR. Your empties should eject at about 3 o'Clock to 4 o'Clock, and you should get reliable stripping & feeding of the next round. If you over-gas your action, it is entirely possible that you fail to feed the next round - this is true of every semi-auto that is gas operated and some that are recoil operated (eg, the Browning A-5). If the action cycles too fast (from being over-gassed), the first round extracts/ejects (with quite some force, I might add) and then the bolt passes over the next round from the magazine - the bolt is cycling too fast for the spring in the magazine to feed the next round up into the path of the bolt.
If your AR is short cycling (ie, ejecting at about 2 to 3 o'clock, and not stripping the next round), you need to enlarge your port by .005 at a time until it reliably strips and feeds the next cartridge. Then you're done.
You should always start smaller than what you expect the final size to be - if you over-gas the action, all you can do is put a heavier recoil buffer into place, and that's a pretty feeble solution, IMO.