Roof space under the perforated panel

The credit requires you to have at least 75% of the roof surface meet the SRI requirement. If I understand you correctly, then the mesh is only 20% solid, so this alone would not meet the requirement and at least part of the roof would have to comply. There are several CIRs under earlier versions of LEED that can give guidance on weighted calculations that take the shading into consideration. Ladders and other appurtenances are not required to meet the SRI requirements.

There are two different questions here (unfortunately). The first is whether or not the roof has much impact on UHI. The second is how you're supposed to treat it for the LEED point. You're probably right that the concrete roof surface doesn't play a big role. For LEED, you still have to document that you're mitigating the UHI effect -- if not by the conventional mechanisms, then by an alternative compliance path that is equally or more stringent. The simplest way to do this is to determine how much of your roof is not M/E equipment, and make at least 75% of that area cool. Part of this strategy may also include making the mesh cool as well (e.g. painting that white). I definitely recommend checking out the different CRIs for more specific guidance regarding the shading -- you'll better be able to figure out what applies to your circumstance.