Okay, for starters go find FSSC (Flight Simulator Scenery Creator), which is one of the best freeware tools I have found for creating airports and such in FS.  For further editing of said airports (AI taxiway use, control tower freqs), I use AFCAD which is another freeware program, and has a new version which allows you to edit visible stuff as well as non-visible.  Check out both of those and then get back to us.

To create your own macros, EOD (easy object designer)
is a brilliant little program.

Here is the website:
http://www.echos.ch/eod/

AFCAD currently can't control buildings etc. but in the future it will. If you want to add some general buildings around the place, Rollerball's package allows you to place objects from the FS library. Pippin has made a nice picture package to help in Identifying the objects available.