@Rhiannon58 Sandrelle is still building for Sims 3 and is active here on the forums. I'm sure Sparky is correct that she wouldn't mind answering some questions. That lot is still available for download on the Exchange, too. I know you're building one yourself for your challenge, but I was thinking, if you downloaded it and placed it in a new or different save of the same world and lot, you could take a look at it and probably figure out a lot of what she used and did. Actually, I guess it doesn't matter where you put it, but I was thinking you might not want it to be in the world where you're playing. The download description says there's no custom content and very little store content used, and I don't think you're seeing that in the siding. Here's the link for it: https://www.thesims3.com/assetDetail.html?assetId=8775555 .
I think the dark blue vertical siding is one of the Pets barn wallpapers - thinking they're in paneling but could be wall sets or miscellaneous. I can try to remember to check that when I go in game this evening.
I know what the horizontal light blue is (or at least I'm pretty sure), and it will surprise you. In paint wall coverings, one of the less expensive choices that appear there has a very light colored horizontal wood on the bottom half and some dull green stuff on the top. If you recolor the wood on the bottom to get that blue - or another color you like - and then copy that to the other channel for the top of the wall, you'll get what you see on her house. You can also use the same wallpaper to make a wall that's stone on the bottom and siding on the top, which may be what you see there on the side of the house (I think that's the garage, but I'm just looking at the front view right now so not sure).
I think the vertical light blue is probably done similarly - maybe with a plain wall (as in no sections, borders, molding) recolored to a vertical wood pattern from the woods section in CASt. If you're trying to save money, you can use the pool wall tile in tile wall covers and just color the border at the top the same as the bottom with a vertical wood pattern. Actually, you can make that wall into all sorts of things.
As for attached garages in houses with foundations in Sims 3, that's not all that easy, I don't think. You need to use CFE (constrain floor elevation), and I have never used it - it scares me. LOL There are a lot of tutorials and videos out there on how to use it if you want to google it to get an idea.