Is it a roof-1?

Seems to me that this is a roof, or at least 80% of it is. The only reason that makes me think twice is the fact that it's at grade, but plenty of roofs are at grade.It seems like a vegetated roof—can you argue for that?

The part of the roof that is over occupied space is definitely a roof, not hardscape. If the pavers themselves do not meet the roof SRI requirement, then you might consider an alternate calculation method in which you borrow the method from the non-roof credit and apply that to the roof credit -- but this is just a suggestion; I don't know exactly how GBCI would respond. I don't think you should count the pavers as a green roof, although if you have exposed soil/vegetation (at the roof level, not the tree canopy) that should qualify as a green roof.

similarly, we have a parking garage under ground that has a roof that is insulated and vegetative. The roof however is at ground level and looks just like a plaza if you didn't know there was parking underneath. is this considered a green roof? i assume if we count this as green roof, we do not count this as site sf.?

This sounds like a roof to me, given that you’re required to ventilate an underground parking garage. In theory you could have decided to use a regular (non-green) roof, so you should get credit for doing the right thing. You are correct that this would not be counted in the non-roof heat island credit. However, you can count it toward other relevant site credits if you meet SSc2, the density/community connectivity credit. You may be able to make a case for that even if you don't meet SSc2, though I don't have any direct experience trying.

This approach is now memorialized with LEED Addendum #100000972. It reads, "Roof area is the area of the uppermost surface of the building which covers enclosed Gross Floor Area, as measured when projected onto a flat, horizontal surface (i.e. as seen in Roof Plan view). 'Roofs', or portions of roofs, covering unenclosed areas (e.g. roofs over porches and open covered parking structures) are not included in the areas used to evaluate compliance with SSc7.2, though they may be applicable to SSc7.1." Also, LEED Interpretation #3126 clarifies that terraces over setbacks in a building are part of a roof, and Interpretation #2293 clarifies that a deck over unenclosed parking is not a roof.