Stone floor tiles are too heavy to be supported by wood so use iron wood beams to support them if not a stone structure or off the ground.

Cooking fire in a tree house:
https://steamcommunity.com/sharedfiles/filedetails/?id=2792152344

Iron wood beam support underneath:
https://steamcommunity.com/sharedfiles/filedetails/?id=2792152359

Chimney at back of tree house:
https://steamcommunity.com/sharedfiles/filedetails/?id=2792152372