I'm trying to estimate a service size for a samll office building. My estimate works out to 10W/SF. Previous projects are all around 10W/SF. It is for a 14,800 square foot building for which I have preliminary floor plans for a small part of it (two tenents). 12 W/SF sound right? There is an elevator which I will add on top (of the 12W/SF) along with other house loads like exterior lighting.

I imagine that much of that load will be computers and such with really bad power factors and drawing current with lots of harmonics. Which means you'd need individual neutrals or superneutrals to handle it.

Make sure that the HVAC loads aren't coming out of your 12 W/SF. They can eat up a lot of power quickly.

The HVAC is included.
By NEC lighting is 3.5W/SF and receptacles 1W/SF (off the top of my head). In practice receptacle loads are higher (at least 2W/SF). Lighting will be less than 2W/SF but (as far as I can tell) we need to use the 3.5.
Electric for HVAC is fairly predictable.