Hi Leif,
I think 4 oz is way too thin - it's not 1/8", it's more like 1/16" and is about as thick as a quarter. The lightest I'd go for an IWB is 6-7oz. However, I personally feel that 7-8oz is a great all-purpose weight, although if the gun is on the heavy side, I'll step it up to 8-9oz for belt-worn holsters. The 7-8oz
is 1/8" thick.
The hardest part about making effective holsters for the full-sized Glocks are the fact that they are thick all over and the grip has a swell in the butt. You're going to want to build something that really brings the butt in to your body since you're looking for concealment. This is done by using some type of fastening method behind the triggerguard (be it loops, slots, whatever). If you went with a Summer Special style holster, I think you'd have some slop from the grip trying to roll out.
For hobby stuff and your own personal needs, you should be able to get everything you need from Tandy. I would think your minimum list should include:
1 single shoulder of 6-7 oz or 7-8oz veg tan leather
1 pack of saddle stitching needles
1 pack of waxed thread (not artificial sinew)
1 overstitch wheel @ 6 spi (this will help keep your stitches spaced evenly over the whole piece)
1 Edge groover
1 Freehand groover
1 Edge beveler (#3)
1 cake of beeswax
Some type of glue like contact cement or Barge's cement
Some dye (for the love of God, stay away from Eco Flo dyes at Tandy. Buy some Fiebing's Pro Oil dye instead)
If you have a Dremel, it would be very handy. You'll need a small 1/32 bit and a sanding drum.
I wouldn't think twice about buying the tools, because after you make your first one, you'll likely be hooked. I make my patterns different than JT, but it's all the same when it comes to gluing 2 pieces of leather together. After that, it gets different again!
After your pattern is made, glue it together. After the glue is dry, sand the edges with the Dremel. Your just trying to even it up, so set it on a low speed and take your time and use long continuous strokes.
Bevel the edges all around, then run your edge groover around the edges of the holster. Your stitches will sit in this channel and will protect them by being slightly inset, and also give you a guide.
Use the freehand groover in the middle of the holster where the stitch lines are.
After the grooves are in there, run the overstitch wheel through the grooves, following the stitch line. The dimples that the wheel makes are the spots you will use to drill your tiny holes.
Drill each hole (a drill press would be ideal) while keeping it as close to 90° as possible.
Now is a good time to dye, particularly if you're dying black and want white stitching. After you've let the piece sit and the dye is dry, it's time to stitch. You're using the saddle stitch method shown here
After you're stitched, dunk it in hot water for a quick second and let it dry to the point where it feels cool to the touch. Insert your gun (UNLOADED - CHECK IT!) and start pressing the holster with your thumbs, following the lines and contours of the gun. I don't put anything around my guns (like plastic wrap) when I build holsters like some people do. After all, your not going to be carrying your gun around with plastic wrap on it, are you? At this point, I use various tools to deepen the impression in the leather - anything smooth that you can find around the house will do. This is done to help push the leather into all of the crevices and voids in the pistols' profile which ultimately leads to good retention. After your done molding, let it dry overnight (I sit mine in front of a fan, usually).
Now you have a stitched, molded holster that's ready to have it's edges dressed. If you don't care about this part, then you can move on to the topcoat. I think it's necessary, but I'm sure there are many that don't. Anyway, your going to lightly dampen the edges with water and rub them briskly with the barrel of a Sharpie marker or something similar. After they start to flatten and smooth out, rub the beeswax on and do it again. This is called burnishing. Do it all the way around on every edge of the holster. This helps keep the 2 edges together, as it almost fuses them, and looks better than anything else you can do to the edge.
Topcoat - I like resolene, some like Neat Lac, Super Shene, etc. Either way, apply per directions on the product. I cut mine 50/50 with water and use lighter coats because with as with any acrylic, too much will get tacky and plasticy.
Good luck!