When I first started I bought a lot of accessories that I didn't really need or it wasn't practical.
First purchase:
Tree Stump Hideout - They like to go in, but they would always get into argument who gets to go in. It had one entrance/exit, not good with Guinea Pigs. No circulation especially on hot days
Pigloo- Same thing, one entrance/exit. Got into argument when one piggie was already in and the others wanted to go in too. No circulation on hot days.
Wooden House- Not fan. One entrance/exit. Urine stains on the walls, kind of small if you have adult piggies.
Snak Shak Log- didn't read what it was made out of, but it took my piggies 1 1/2 year to demolish one. As long as they don't eat it constantly then I think (IMO) it is fine. I like to fill the top hole with hay and use it as a hay holder also can be used as a tunnel.
Snak Shak house- different from the log. It had the straw roof which was really hard and was afraid it poke my guinea pigs mouths so returned it.
Best bet: save your money
with purchasing the houses. You can use cardboard boxes and cut two or three entrances (piggies loved) and you can always throw away when they urinate on the walls. You can make a fleece tunnel using bent grid square and cover it with fleece. Or a fleece house.