I respect your intentions to create a 3D representation of this private property (probably your home), however, your usage of OSM tags partially counts as tagging for a specific renderer, F4map in your case. Consider: https://wiki.openstreetmap.org/wiki/Tagging_for_the_renderer

Also look at my changeset just before this one for better context: https://www.openstreetmap.org/changeset/162656640

I commend the geometric level of detail, but I want to express my opinion (which might be flawed) about some tags:
1. Instead of landuse=driveway, better use area:highway=service and something like area:service=driveway to draw the area of an access road. Plus, you should also draw the center line, in this case highway=service with service=driveway.
2. The key height=* should not be used for the elevation of the steps relative to “the normal ground” – or maybe it should be? Not very sure about this anymore; I did change height=* to ele:relative=* in my first changeset, though.
3. Regarding the structures in the garden, which you mapped as building=portal with 3D building tags. I didn’t touch these, since I realized a conflict of interest: building=* is not fitting for such a structure (something like man_made=portal fits better), but only building=* has such an elaborate 3D mapping
4. The main topic of discussion: the staircase. It’s really diligent of you to map every single step as a rectangle, but building and building:part are really not the right tag keys for this since staircases are not buildings by themselves – they’re highways. For that reason, I changed each of the steps to area:highway=steps and the level parts of the staircase to area:highway=footway. After doing that and adding highway centerlines, I didn’t see any purpose in the enclosing building=stair polygon and deleted it.

Tagging in OpenStreetMap can sometimes be complicated and both of us having differing opinions is perfectly normal.

Have a nice day!
— keepright! ler