Wow... our builder (Bavaria) asked for double that. (masonry double garage 6.5x9m with floor slab and gable roof) --> We left out the garage for now.
Think it over carefully, later the fun will cost even more and you'll have to start over.
Planning and approval are done by our architect, that doesn't add much more cost. I once broke down the costs somewhere.
The shell builder makes the floor slab and builds the garage. By the way, it will have a flat roof. For that, we pull out our ground floor and let it rest on the garage. On the south side, there will also be a balcony. So the statics are not that simple. We have the windows and doors quoted together with the house. The plastering will then also be done later together with the house. Surely you can start again later and plan a garage attached, but I would think about it three times.