I make my own gear for 2 reasons:
Every piece of hiking/camping/backpacking gear I've ever owned I've found aspects that I maybe didn't love, or wished would have been made differently. I find this with almost 100% of consumer goods, at least the ones I haven't designed (I'm an engineer). For this reason I make my own, not because it's guaranteed to be 100% perfect and how I wanted it, but because when I find aspects I don't love, I know how I made it initially and therefore have a better idea of how to change or improve it.
Secondly, I just really enjoy being able to use something I designed and built in the hobbies I enjoy. This is definitely not limited to hiking/backpacking though, I like to design and make things for a number of my random hobbies. Seeing something I made in action, or having someone else on the trail remark about a piece of gear I made, is very rewarding to me.
As was said above, versus buying used gear, there might not be a huge opportunity for savings, sometimes the opposite if you screw up a couple iterations before getting it right, but the end result for me is for sure worth the money and the knowledge gained.