This weekends project:
Run some Cat 6 network cable through the house upstairs.
I have the plan in mind, but one thing that sorta stops me getting started is
Im a lazy **** I'm not sure how to run the cable up the inside of the existing walls without destroying them - past any noggins that will be there.
So the roof looks something along these lines.
Was single storey house, then had addition added along the lines of this one - I wish to **** my house did look like this, but alas it doesn't.

I wanna run it up the wall from the ground floor, into the roof cavity then #1 son (who doesn't know it yet) will around and about.. but getting it up the wall has me a bit perplexed.
Going under the house isn't that easy either as its a 40yr old house that has been built onto as the original owners family expanded... so you cant get under the house from side to side easily either

If I could, it would be a cake walk!
So, any hints on how to do it easily?
Thanks