I think this can work really well for smaller houses, though larger ones can get out of hand fast.
The "method" I've used to recreate / work off of RL floorplans is I base things on some of the furniture, knowing how many squares they take up in game, and start "measuring" based off what I know. This helps keep the house in a scale for Sims, while also keeping the ratio of the rooms consistent.
So I look at things more like this:
https://i.imgur.com/KWvyBAB.jpg
Here is a base house I just grabbed offline. I know that a stove and sink are both 1 square. I know each counter is 1 square. I know the laundry stuff is 1 square. I know tubs are 2x1, toilets are 1, double doors are 2x1, fireplaces are 2x1, and so on. I mark these off either in an art program, or just mentally.
Once I get a feel for one room, also taking into account how sims move (needing .5 space around things) and the flow of buildings, I do this:
https://i.imgur.com/ymmNktI.png
Once I'm in game I can decide if I want to push or pull rooms around a little to make them bigger or smaller, but take the dining for instance - 5x5 is lovely for a cozy dining room. A table is 1x3 normally, with chairs on both sides it's a 2.5/3x3 - giving 2 squares of space around each side of the table for decor or walking room.
The bedroom is 7 wide, so a 2x3 bed will fit in there nicely, with room for many other goodies. That 3 wide window pop out on top can have a bed right in the middle of it. It feels sims-scale, though there's always freedom to move things around. Even the stairs scaled in appropriately once I got a feel for the kitchen space. (normally where I start, or a bathroom!)
This is the easier method for me because I'm very visual, and I'm terrible at math. So this helps me get a quick handle on scale without worrying about weird numbers at all.
Happy building!
