Cutting angles when components meet in converging planes

Hi there
I am a complete beginner and have modelled this form which will be made out of 12mm particle board.
Each of the faces has been saved as a Component, with the exception of the largest piece which is a group.
Particle Board Form.skp (127.2 KB)

My aim is:-

  1. To take the bottom edge off all the groups so they are level with the Guide line which runs along the bottom of the internal vertical support piece.
  2. To remove the excess off each component where they join so that I can measure the angles of all the different pieces
    where they join.
    I have looked at the Tutorial on creating angles Using Sketchup to Create an Angular Mini Shelf - YouTube but in my model the components have converging lines. All help would be greatly appreciated!!

Would you be interested in a live demonstration showing how to do this? I can make that happen.

I would be very interested!

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