Hey Dakota, I have made many, 50+ kydex holsters, put in the oven at 200 f. will come out limp and pliable, my preferred method is with an industrial heat gun, then a bowl of cold water and a wet towel, once you heat the section of kydex you want to form, press it around the firearm, and shape it, once it is shaped, use the cold wet towel to cool that section down so it sets. The wet towel is more of a hazard than the heat of the kydex on your firearm, remember to keep it dry and clean it afterwards. The only other warning is once your at the stage where your molding while the firearm is in the holster, the heat from the heat gun, can affect plastic pieces like Glock sights and nylon or rubber grips, so keep that in mind.
To start making holsters, I use thick paper like used for the backing on a legal pad, matting I think they call it. Place your firearm on the paper and trace it out on both sides, pistol laying left and then gently roll it over to pistol laying right. This is your base, then decide what kind of holster you want, IWB, OTWB, cross draw etc... I use .060" thickness for IWB, and 1/8" for OTWB. Use the paper to make a mock holster, it will bend easily and you can see your concept beginning, form it around the firearm. Once you have made a paper holster to your liking, use that to trace the design on your kydex, now start heating and molding, kydex is pretty forgiving if you don't OVERHEAT IT, if you do, it will blister and change to a harder state that is brittle.
Once you have what you want, keep that paper template and label it for future use.
I still have a kydex IWB for my 5" 625 S&W, people can't believe when I jerk that big gun from concealed and it is comfortable. Just the right length that it does not bottom out when sitting down or driving.