Complex pedestrian bridge

Hi Mcarton -- Since these are private indoor areas and will not be used for routing, I'd probably just be inclined to draw them as parts of the buildings, or make them an entirely new building themselves. Just tag with layer=1 and they should not interfere with the road and walking paths. They don't seem to be present on the aerial imagery yet (here's the area in question) so you may just have to guesstimate.

Edit: Adding the bridge=yes tag, as suggested by the "skyway" answer linked by neuhausr, is also a good idea.

It might be satisfying to try to show how high they are and where on the buildings they connect using the simple 3D building scheme. You can draw a bridge in several parts to show its incline from the first floor of one building to the second floor of another -- eg, first a segment with min_height=10 and height=13 meters, then transitioning to a segment with min_height=11 and height=14, etc. This will work better if your buildings are tagged with height, and you may want to add a building=yes or building=parking tag (as well as height) to your parking structure.

You could go all out and try to apply the indoor tagging scheme but again, since these are private areas, it would probably be a wasted effort.

This sounds a lot like a skyway--see the answer to How do I tag a skywalk / skyway / skybridge for the way I've usually seem them mapped.