Ah, the Housebuilder extension. And a bit of misunderstanding about the way plugins can be installed. The plugins/extensions are still .rb (two letter file extensions) but most of the plugins now come with the three-letter extension, .rbz which is a package that the automatic installer can read using Install Extensions from Preferences/Extensions. There are several reasons for that and I assure you, they are all good.
If you are coming from SketchUp 2013 or earlier, it is important to avoid simply copying plugins from the older installation to the new one. There was a change in Ruby because the old version was no longer supported and most of those old plugins won't work in the newer version. So install fresh copies when you do. Also, do not put them in the Plugins folder under the SketchUp application. They go into a different location now.
Where did you get Housebuilder from? The versions in the French Ruby library have not been updated to work with the new Ruby version.
As for drawing in 2D, you can do it if you must but it requires making copies and rotating them for the other projections. If you must work that way, I think you should be using a 2D drawing program instead of a 3D application.
What tutorial are you referring to?