I guess the new 4.0 version did not give any progress for roofs?

No, maybe in a coming version...

Currently I feel like SweetHome3D(SH3D) is good for flats and multi-stage flats, but not for houses.

Keep in mind that Sweet Home 3D first targets interior design.

What is the current state for house environments such as gardens?

Gardens would require some "terra forming" tool to give the various elevation points of the ground, and more models of plants and trees. This kind of 3D models are complicate to design, so it will take probably years before a complete library of this kind appears, according to contributors proposals.