A while ago helped another friend wire up his whole house during contruction (about 5-6 years ago) and while we pretty much ran most of the cabling there were a few spots where we just put flex tubing in for future wiring. Today in my home I have built a "run" from the basement to the attic. I leave a piece of non used CAT5 in the run for more cabling (which I have used a few times since the initial runs were put in). For the second floor in my home all of the cabling goes to the attic via the one run then to the bedrooms/bathrooms,ceilings/walls. In the main floor of the home all of the cabling goes from the basement up into the walls of the main floor. The ceiling devices go over to the top of the wall 2X4 then down the wall. I soldered every connection. I have about 1.5 feet of space above my ceilings on my main floor. I used a lot of CAT5 but for the doors and windows switches I used 16/2 plenum rated cabling. It was easier to run cuz its so small. Basically every sensor is in its own zone (a bit of overkill) but it gives me a lot of flexibility with HA. It is using more wiring than multiple switch loops would use. When my children were young I had a TTS panel and utilized this to give me some feedback to what door was opened or closed.