Hopping Hammy has a video making one out of melamine, plexiglass and aquarium sealant - have you seen that? She used an upside down table as the base and corners. I did think about something like that with one of the larger Ikea Lack tables but the amount of diy puts me off (having doors to fit and so on). Also at the end of it the cage isn't that much bigger than a commercial one and there are some good, affordable, commercial ones at 100cm. I think the one Hopping Hammy made was much bigger than that though.
The Germans reckon melamine is ok because the chipboard/formaledhyde glue in the chipboard, is encased in the melamine and the melamine wipes easily. I remember a German member saying for larger habitats they use the Ikea Pax wardrobes which are melamine (not sure how! Whether it is putting shelves in it or tipping it on it's side).
Plexiglass is safe but can work out a bit pricey sometimes, and yes it can get scratched. There is a pet-safe aquarium sealant called Petsafe Ecobond but according to reviews it still has an extremely strong smell and needs a few days for that to wear off before a pet can go near it. (I looked into all these things when thinking about Charlie's upgrade!). I came back to - Detolf or Barney lol. I got the Barney cage and am very happy with it. The Detolf is probably the most diy I'd want to do. It can work out quite expensive sometimes as well unless you have all the right tools. But I'm always very impressed at people who do build them.
It comes down to space and cost I guess, plus a bit of wanting to make something individual/ideal. I also looked at some vivariums when trying to work out how to make a melamine unit with sliding doors, as that is basically what they are! They just need extra ventilation installing. The downside I think is they don't allow for much depth of substrate, and some of them aren't that cheap. I thought this one was a good size
It's 115cm wide, 60cm deep and 43.5cm high - but it's £100!
Discounted: VivExotic Viva Vivariums: Extra Large | Swell Reptiles
So making something like that yourself would be more cost effective. I think the Detolf is probably one of the cheapest diy hacks and gives a lot of space at 163cm wide x 42cm deep.