Leroy Merlin cuts particle boards and laminates the end faces for you, at any arbitrary dimensions (rectangular though). You pick the boards, make the order for cutting with the staff, leave the carriage with the boards, and in 15 minutes they're ready. All you have to do at home is drill and screw the boards together, add hinges etc. (You'll need a drill director for precision.) So this is doable without any home workshop. I myself made couple of lockers this way.

One example where IKEA hacking wouldn't have helped: I needed a thin (20cm) and short (80cm) locker for the bathroom. Ikea had nothing close to this -- at least 30cm thick and 1.5m tall. So, I searched Leroy Merlin catalogue fr the most suitable door facades (they weigh twice less than particle boards of the same size) -- and designed the locker around them. We've been using it for 2.5 years.

In the UK at least, furniture panels from B&Q, Wickes, Selco, etc, are very much inferior to the stuff some IKEA (e.g. METOD and PAX) furniture is built from. That was why I used PAX carcases to create built-in wardrobes. Plain furniture panels would have been lower quality.