I try to heal you model, but let me some time, I try to add line to close your floor, you have to know when you create a model, take your time, and do a save, for example object_00.skp, and 01, 02.
If you do that, you can come back on old project.
I hope my advices are useful.
About savoirpourtous, I created a channel and a web site where I speak about Blender, Inkscape, Gimp, Sculptris ans so one.
All software are free (I like to share knowledge and culture)
And to finish, a few videos on Japanese but just for the fun