technically this could work. in reality, without addressing all the reasons its a bad idea, quite simply I don't even see how you would get 20-22 gauge into most standard XLR plugs. it would be cheaper, better and quicker to buy 100ft of decent cable and 16 male/female XLRs, or whatever you need, and solder those up.

And you can NOT use speaker wire to run microphone signals. You need shielded two conductor microphone wire.

You could get away with using a 16 conductor with ground cable and it could be 22 or 24 guage, but it's better to have individually grounded and shielded pairs. Do a search for audio snake cable. Keep in mind you would still need to solder 8 male and 8 female ends to the snake.

I personally would check out Hosa snakes. Much less hassle and most likely a better product.

I think Jeemy is right that this could work technically (and by that I mean theoretically), but you would need to make sure any any EMF meaning amplifiers, power cords, light bulbs, computer monitors are kept away from this line. It is cool you want to isolate the drummer and the best way is to seperate them from the band for recording in real time. Some bands create a drum booth which is nice because it can double for a vocal room or for solo work. Other bands create a half wall that cuts down on the bleed but does not eliminate it completely. I remember one project where we foamed a bathroom in for this same type of isolation. Anyway from what I hear you would want to wrap the whole line in foil in a criss cross pattern like braiding. This foil also needs to be grounded. The bad about this is that if it does not work and EMF gets in you not only have buzz and noise but you have it x 8 which would be super bad. Add to that the foil could instead of insulating could act like an antenna and you got a wall of noise.

That being said, reinventing the wheel is a bad idea and you should just break down and figure out a way to horse trade for a snake if you want to record the band live. You also should get a multi track recorder and record each part individually imho. Recording multiple peices at one time is super frustrating because everyone has to be perfect in time and execution with no bleed. It just doesn't happen... It is easier to record the guys in headphones with the guitar player playing in the headset of the drummer while tracking the drummer to build the timing of the tune to record the other tracks around.

To say you cannot build a shielded snake on your own is not realistic because shielded snakes do exist and obviously they can be made. The question is whether or not you are willing to put in the time, energy, and money to reinvent the wheel?

Either buy a proper snake or by a multicore piece of wire. If you run your green wire in your proposed setup, do not connect it to any xlr. Attach it to the rack ground on each rack but it is not advisable. Again, just buy a piece of 8 core snake wire and solder the balanced connectors you need.