Do you have to go around the board once to purchase properties?
Sounds like a house rule to me.

http://richard_wilding.tripod.com/monorules.htm claims to be a copy of the rules from the official rulebook.  The section on Buying Property reads only:


  Whenever you land on an unowned property you may buy that property
  from the Bank at its printed price. You receive the Title Deed card
  showing ownership. Place the title deed card face up in front of you.
  If you do not wish to buy the property, the Bank sells it at through
  an auction to the highest bidder. The high bidder pays the Bank the
  amount of the bid in cash and receives the Title Deed card for that
  property.


Nothing about having to go round once, and certainly I've never played a game of Monopoly in that way.  What would it even achieve, apart from slow what is already a potentially long-winded game down to an even more glacial pace?