Not a good idea, unless you can verify the composition of the insulation on the jumper cables. Look for the gauge markings on the insulation (probably just an embossed printing that is next to invisible to the naked eye) and see what else is stamped in there along with the gauge. If you can tell that it is "Primary Wire", or a cross linked type, then maybe it would be worth proceeding.
Here is a quick look at some common automotive wire types and their three letter designations which you would be looking for:
https://www.awcwire.com/faq-automotive-wire
There are issues of abrasion, temperature resistance and oil resistance which automotive wire must be able to withstand, but not jumper cables. Jumper cables are not intended to be a permanent installation and as such are not likely to be designed to withstand everything that is going to be thrown at a wire that is permanently installed.
And imagine what happens if you short out your battery cables. There is no fuse in place to protect you from that situation.
If you want to build your own you would be better off going to Napa and buying new cable by the foot. They will have the right material, and probably a selection of gauges.
Sourcing the right crimper and the heat shrink with the glue inside would be a good idea too, but once you get to that point you are probably better off just ordering a set of custom made battery cables from someone who is already set up to build them. OTOH, depending on where you are located, there may be someone around who has the tools and would be willing to lend you a hand. There was a crimper sold in the SoCal "For Sale" section a couple of years back. It wouldn't hurt to ask around.