I love how you bought books full of floor plans! I tried floor plans a little bit, but the floor plans can become a little overwhelming to look at. I tend to look at pictures of house exteriors, and I'll create something that derives from it. I am more freeform with the interior and I will create a living space with the space created by the exterior.
I find when trying to build a replica of a real life building, a grid unit is equal to 1x1 meters or 3x3 feet. Of course many real life houses don't follow the grid format. I've had difficulty trying to match stairs in the game, as many houses have steep or winding stairs. I've also had difficulty (more so in sims 3) to build garages with a foundation. Sims 4 is so close, but we just need a garage door that goes through the foundation. Sims 4 has also been much better than sims 3 with putting functional objects closely together, such as in a bathroom. Many times toilets are right next to a bath tub. It's also a nightmare trying to accommodate split leveling.