Monopoly houses bidding?
The rules for monopoly are pretty clear on this point (emphasis mine)


  BUILDING SHORTAGES: When the Bank has no houses to sell, players
  wishing to build must wait for some player to return or sell histher
  houses to the Bank before building. If there are a limited number of
  houses and hotels available and two or more players wish to buy more
  than the Bank has, the houses or hotels must be sold at auction to the
  highest bidder.