How can I merge sketchup files together?

I have a file for my kitchen/living room (which is pretty basic, just the outline of the room with the plans for my kitchen bar idea), and I designed a window seat that I wanted to incorporate into my living room design that I did in a separate file (because I didn't want to mess up the other file-- since I'm still learning how to use the program and prone to mistakes). Is there a way to make my window seat plan into some sort of object that I can insert into the other plan and keep the same dimensions/scale? Or do I just have to redraw it in the other file?

Also, is there a way to use the program to calculate square footage on say a floor plan? I wanted to see how much flooring I'd need to plan for after I placed in my new bar and window seat, as well as the existing cabinets, in the design. I could do it manually, but thought the computer might do better math than I do. LOL!