I generally craft my own amps nowadays, but I'll agree with the others that it's generally better for >95% of miners to buy their amps, especially since shop user shops have them cheaper than auction. PA Mall, Medusa, and Twin Peaks Mall all have amps under auction MU depending on what you need.
That said, if you are going to mine with your own crafted amps, level 5 or d-class are really the starting point you should consider it (a case could maybe be made for a level 3 MU-wise, though I'd just say buy level 5s at that point). You should be able to pencil out the rough predicted MU of crafting an amp and relatively compare to others to see which ones have the lowest MU costs. Those should be with high QR bps though (ideally 90+), and for say a level 5, that should at least be running you around 1k ped.
The trouble is needing sufficient bankroll to craft a large number of amps at once so you don't get caught in low sample size variability. Part of that is just having the main crafting materials, but the challenge is having enough residue on hand at a sufficient price. Back when residue was 101%, I could make a case for crafting amps being a better deal, but lately, it's been closer to breakeven for me with shop prices unless I can bid on really large lots that have lower MU.
I started crafting level 5's with a QR 90+ bp in the last year, and my current cost per amp including globals and HoFs is 199.25 per amp over about 500 clicks. If I don't include those multipliers though, then I'm around 204 ped in cost/amp. That's with high QR and very low residue costs, reusing residue from my amp crafting, and generally paying decent auction rates for the other ingredients since I don't want to confound my mining accounting. I still feel like I got really lucky though, so I'm not considering 500 clicks a large enough sample size to be comfortable with my numbers. That cost/amp is creeping up now that I've eaten up my <101% residue I stored up though.
I also have been working on a D-class bp that's around 20 QR now, and I can definitely tell that low QR is eating up the PED. Part of it is starting with higher residue costs from the start, but I'm mostly fighting to keep my cost/amp even with what I can sell for on the auction while I "train" on the BP for more QR. I'm better off buying D-class amps for mining still though unless I get a good global or HOF to push the cost down below 103.75% (the cheapest D-class amps I've found for sale).
So it is possible to get ahead crafting your own amps, but the market on residue is so tight, and you don't really stand a chance in the near-term with a low QR bp. I'd say it's easier to end up costing yourself more crafting than the auction/shop cost even if you're being semi-careful than coming ahead even with my success on level 5's so far.