I once wasted a day trying to lay out a building and parking on a site. It couldn't be done. The building footprint, plus parking, plus zoning setbacks equalled 92% of the area of the site. Tight, but do-able you are thinking; just get creative.
... Did I mention that the shape of the site had an offset that prevented an efficient parking layout? Some layouts came so close to working that I was sure there was a solution. Nope, the math wouldn't give.
If only I had worked the math first, I would have spent most of that day looking at alternatives like partial two-story, or a full two-story building, or simply explaining that we were wasting our time on this site.
This experience put me on the alert. So when a client wanted to know how big of a building would fit on his site, this spreadsheet was born.
First I set up some fairly straightforward calculations for determining the area needed for parking. Next I looked at the impact of adding more stories would have. Finally I addressed the limitations that zoning puts on projects - setbacks, height limitation, parking requirements. That is when I realized that this problem requires sophisticated math to solve - but fairly unsophisticated math to get an approximation. So into the spread sheet you put various guesses. The answer you get tells you what your next guesses should be. After a little trial and error you have better information than a half dozen schemes.
The second part of the spreadsheet reverses the problem. How big of a site do you need for a building of 'X' SF?
In both cases some knowledge of site topography and building characteristics are critical. For instance, a site with too steep of a slope could be difficult to maximize. Or a three-story building with only 5,500 SF per floor might have less useable SF than a one or two-story solution because of the space tied up in steps, elevator, toilet rooms and even exterior wall thickness (multi-storied buildings have a higher ratio of exterior wall to floor area). Math doesn't tell you this, experience and common sense tell you this.
Math and especially spreadsheets can be timesavers, but a calculator has all the math you need to know.
The actual spreadsheet is available for download here.
Other tools might be helpful:
Trello-PM - project management system
FeeCalqs - fee estimating system
OFFPLAN - work load projecting system
MyCorbu - timekeeping and project bookkeeping system