The Collaborative International Dictionary of English v.0.48:

buildup \build"up\, build-up \build-up\n.
   1. the act of building up an accumulation.

   Syn: build-up.
        [WordNet 1.5]

   2. the events, such as advertising or publicity, causing
      increased interest in some coming event. The buildup to
      Superbowl XXIV was the most intense of the series.
      [PJC]

Moby Thesaurus II by Grady Ward, 1.0:

103 Moby Thesaurus words for "buildup":
   access, accession, accretion, accrual, accruement, accumulation,
   acknowledgment, addition, advance, advertising, advocacy,
   advocating, aggrandizement, amplification, appreciation, ascent,
   assemblage, assembly, augmentation, ballooning, bloating, blurb,
   boom, boost, broadening, bruiting, building, combination,
   commendation, composition, compound, constitution, construction,
   crescendo, development, drumbeating, edema, elevation, embodiment,
   enlargement, expansion, extension, fabrication, fashioning, flack,
   flood, formation, gain, getup, good word, greatening, growth, gush,
   hike, honorable mention, hype, incorporation, increase, increment,
   inflation, jump, junction, leap, make, makeup, mixture, mounting,
   multiplication, organization, piecing together, plug,
   press-agentry, productiveness, proliferation, promoting, promotion,
   publicization, publicizing, puff, puffery, putting together, raise,
   recognition, rise, setup, shaping, snowballing, spread, structure,
   structuring, surge, swelling, syneresis, synthesis, tumescence, up,
   upping, upsurge, upswing, uptrend, upturn, waxing, widening