Rob
Ansys Employee

I find it's easier to create the main fluid volume and then subtract bits to form the voids afterwards. Don't just rely on the tools doing everything in one step. If you hide volumes in SpaceClaim geometry operations don't effect them, and you can then use those volumes when you unhide them. 

Named Selections in SpaceClaim are useful for going into Fluent Meshing. Otherwise, use the tools in Ansys Meshing. But, you do need the room volume before switching to meshing. I'd also lose the "thick" walls unless you REALLY want them. If they're for thermal reasons read the thin wall options in Fluent: I've never included walls in Fluent HVAC models as anything other than thin surfaces.