There's already loads of underground car parks. There's also a car park in front of the skyscrapers in the left of that image. The 4-lane tunnel runs underneath the property as well. I came up with this rough, initial idea last night:200%
The big kite-shaped building is just a rough base. I intend to give it somed exposed structural features, perhaps some big metal frames and suspension bars around the outside? Very modern and stylish.
The dotted line around the hood to the tunnel is where I suggest the corporate landscaping should be, roughly. The circle areas are little rocky pools set into the side of the slope and the circle on top is a fairly steep ridge, so that you can do huge jumps if you get a good approach. If myself and Snow Racer can get the geometry right, it could become a unique stunt bonus which makes you land in/on one the building balconies, or lets you smash through a window. Or something.
The collection of odd shapes next to the car park are the small shops SR wanted. The dot is a fountain. The road to the car park is quite narrow and has no pavements. I think I might have it have a junction which heads behind the building, sort of like an "employee's" area, or a supply access type thing. Again, I havn't worked out the detail.
(EDIT) I really need time to work out the detail of these sections, this is very preliminary - only a few hours of my thought has gone into it so far. This is a very complicated area because of the landscaping, the cutting-edge architecture and the odd-shaped buildings.