I'm looking for Schematics or Diagrams or Blueprints of NFL Staduims
-- all, or as many of them as possible for a computer modelling
project i'm working on.

I specifically want general layout details, like the height, and size
of the decks, width and height of the staircases, size of the
sections, dimensions in relation to the field, size of the pressboxes,
dimensions of the entrance tunnels, and so on.  I'm not interested in
wiring, plumbing or things like support beams.  I need the general
structure.

I'm fairly sure that I could go to the clerk of the court or the
utility companies for each of the stadiums, but that would likely be
too research intensive.  Is there a repository, or a collector or
something that has what i'm looking for?

of the last 16 stadiums 10 were build using HOK (Hellmuth, Obata &
Kassabaum) blue prints , your best bet would be to contact them and
ask for the blueprints

http://www.hoksve.com/sport/projects/58DA5A6D-8468-4149-B12F-FFD815A8C908/Alfred_McAlpine_Stadium.htm?sort=Alpha