Part 1: Making the scene
1 - First, I created the two main walls, since they will be the spine of the image. Every other object will relate to them: locations, sizes, etc. I used splines and extrusion for making them, as you can see it in the attached example tutorial. I've spent quite some time with them, because if they are not right, everything else will be a mess and it's a bit difficult to go back and redo a bunch of things. These walls were converted to polygon objects after I felt like they looked good enough.
2 - then came the small roof structures and windows. Mostly I keep my models simple. Some of them are so primitive, you wouldn't believe. But, if they're small in the picture, then why complicate them, which increases the number of polygons.
3 - the roof tiles. I knew I was going to make a bunch of them, so again, I kept them simple. They were done with splines and extrusion. First I made one row for reference, then I built a roof. Then later this roof was used for all of them. Mostly I shaped them with the Slice modifier, or when it wasn't much visible, I just roughly deleted some polygons to speed up the process. Finally I dropped a Noise modifier on each one of them, that makes them uneven, thus quite natural.
4 - as you can see, a lot of other objects were created from primitives. For example all pieces made from wood were done this way. It's simple and fast. Where I wanted the object(s) to be somewhat uneven, not so "engineered" looking, I added some more Noise to them. The texturing was simple too, I just dropped a Box UVW modifier on them and that's it. Where something didn't look the way I wanted, I started changing the Gizmo's position and size. The little tree was made with Onyx Tree Pro, since it's very fast. All flowers in the windows were done with PlantStudio 2, which is a free plant generator and it works quite well.