Sketchup free version only exports to SKP (
.skp) and Collada (
.dae) formats. This isn't a lot of help when importing to Unity, or any other game application. There are several ways to get around this. Providing you have access to more than one computer, the easiest of these is to install an evaluation copy of SketchUp Pro on another computer and use it just for export. This way, the 400 minutes of free use last for ages. I've put some alternative methods in Appendix, MakeHuman.