Thank you Dave for the HouseBuilder_extension.rbz file.
I was wasting time with the rb files and the rbz installed and worked in SU8 after reopening.
HB appear in my Draw menu.

Cannot install HB on Mac (OS 10.6.8) in SU8.01.
I have downloaded HB folder on my desktop containing garage_tour.skp (no model in scenes), HouseBuilder.rb and HouseBuilderTool.rb

I open SketchUp > Preferences >Extensions and Install extension.
I navigate to the HB folder > open and all contents are GRAYED out preventing installation.

I am thinking I should manually install HB and I cannot find any SU plugin folder to place HB into. There is no SU plugin folder in the folder I purchased from SketchUp and I cannot find any SU plugin folder on my Mac.

Any help is greatly appreciated. The HB plugin looks enormously useful.