Homemade hides can be nice if you like doing do-it-yourself projects or just want something unique for your tank. I've made three sets now total. My first set I made was with polystyrene (styrofoam), carving it out into the shape I wanted and using Excavator reptile clay over it. It eventually crumbled on me since I didn't seal it or anything.
The most recent sets I've made (one for my 55 gallon tank and one for a temporary 10 gallon tank) turned out a bit better. I spent about a month on my 55 gallon tank, making two hides, and a wall with ledges in it. I used polystyrene sheets, once again carving them out into the needed shapes, gluing them together with an all-purpose caulk. I let those sit for a few days to make sure they were completely dried and ready to go. I used tinted tile grout (I used the powder kind that you just mix with water) on top of the polystyrene. I did about 4 to 5 layers of it, letting it dry before each new layer. Since my tile grout was already tinted, I didn't paint it, but you can paint it if you like with a water-based acrylic. They are usually non-toxic. Then I sealed mine with a mix of Mod Podge and water in a spray bottle. I did about 4 coats of sealant on the wall and 5 on the hides since my leopard gecko would around them more often and didn't want it worn down and crumbling like my previous hides were. Mod Podge is also non-toxic, but not completely water proof. So if you have a project involving water, I would not recommend using it. I've heard of people using polyurethane though. I just have no experience with that. My hides and wall turned out very nice, in my opinion. They're simple but I like the way it looks (like reddish clay).
The other set I did (for my 10 gallon tank), I made from tupperware containers that I cut a hole in the side for entry. I covered that in air dry clay and when the clay started to crack, I coated it in tile grout, then sealed it with the mod podge. Not the best method, I'll tell you. The tile grout helped seal the cracks together but you can still see that the clay is falling apart through the underside of the tupperware (since its clear inside). Also, I've found air dry clay is not good around heat sources. The clay is non-toxic but it seems to crumble more if you mess with it.
I think styrofoam with tile grout is by far my favorite. If you want to check out Becky Wheeler on youtube, I got some pretty good ideas and learned a lot of things from her in the making of hides and such for your reptiles.
Hope this helps.