Rodipet do sell legs that fit their houses. They’re not great - I find them stiff and fiddly but they’re ok. Before that I just used to use dowels (about half a cm diameter) and glue then on. For that you need to use safe wood glue. Ponal was the one used in German hamster forums so I’ve always used that and it’s very good. Strong enough wood glue to firmly glue legs on but no real odour and pet safe. Having said that, previous discussions came to the conclusion that any glue was safe once hardened and no fumes left - providing it wasn’t visible to be chewed etc.
Despite that I stick with ponal as no fumes - it’s virtually odourless. It’s not as difficult as it sounds either - I’d just have the kegs long enough that they went up the front of the house so a longer area to glue then to (as opposed to just the little round top bit of the legs glued to the underneath ),
Brackets sounds quite fiddly but I guess it’s one way if you have a cage you can screw into - can’t see how that would support all four sides though.
To be honest I preferred my glue on dowels to the Rodipet legs but I got lazy
. I still have a supply of the dowels though - they are cheap to buy - and I bought a tiny little saw about the size of a kitchen knife which cuts through then to cut them to size.
I linked it recently but have a photo of the dowel legs on one of the Rodipet houses. The advantage of them is you can put the legs where you want - it varies due to type of house and type of cage. So for a barred cage with a sloping base at the sides I’d have the dowels at the front and sides with the back resting on the edge of the cage base. If you want the house to sit lower than that it’s more fiddly as you ‘d have to work out measurements for shorter legs at the back so they could rest on the curved base.