Option 1 documentation

There are a number of resources depending on your location.

1. Local on line tax data - usually has building heights and gross sf. and in some locations is searchable graphically by map. Not so useful if you need addresses to search.

2. Zillow.com has some information about homes, including sq ft, and may include land area. it has a graphical interface.

Regardless of the tools and resources you have
available it is likely more of a time commitment than a few hours. Other
options might be to contact building managers and owners directly to
confirm density information or use mapping tools like Google earth to do
some rough take-offs (building
footprint x number of floors) to confirm if you are close to
meeting the requirements of this option. Confirming actual SF through
the local municipality or the building owners/operators would be the
best and most reliable course of action to confirm that your figures are
accurate and will be approved in the design review process. If the
information to meet this credit just isn't available, consider Option 2,
as it is generally easier to document. If you are in a high density
area there is a good chance that you will qualify for the credit via Option 2.

By a few, I assume that you're describing 3 or 4 hours. Depending on the location this can be simple (a county with great on line resources) or more time consuming. We normally do a work plan (with hours required and related fee) to build enough time into our process to pay for these services. I agree that option #2 is easier.