Is it okay to keep my guinea pig cage on the FLOOR?

i have a smallish pet store cage (24" x 24") and i keep the cage door open and attatch my guinea pigs playpen to it for more room. in the outer part i just put down a towel and fleece blanket. i was thinking of doing away with the cage completely and just using the playpen but idk cause i have no floor thing for him besides blanket & towels and my parents wont lemme buy anything else. anyways in the winter the floors are heated. is this bad for him? what should i do? should i just keep him in his petstore cage and put him on a table or use the playpen grids to make a larger cage but keep it on the floor?!?!?!