you can drill into glass as long as its not tempered glass. you need diamond drill heads though
I just built one myself. It literally took me 3 days to complete. Its only a 10 gallon but works perfect. Got the tank for 10 bucks and used acryllic for baffles 4 bucks a piece. Easy to cut. Then used marineland silicone 6 bucks. The most expensive part is the overflow and return pump but you can find them cheap. Definitely worth it IMO. I dont have to stare at my protein skimmer, heater and filter the whole time. I also added some filter media in between the baffles for extra filtration.
Nice rig My only concern with the siphon "powered" overflows is if the siphon is lost...biiiiig mess awaits. I saw somewhere online where someone made a failsafe that basically cut off the return pump if the water got too low in the sump, but I can't find it.
Seeing as how my first SW tank is going to be a 20G setup, having the "dirty work" under the tank, rather than in it, is a big consideration for me. I just need to figure out how to make a failsafe overflow.