Here is what I did, what I find is the easiest way to get this achievement, since it's hard and long to build houses/hotels with human players.
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When you go play a Mode in Richest put the CPU's difficulty at High Skill as that should make it to where they put up houses and hotels faster. The CPU first needs to have Monopoly (which is identified with gold lining around their properties). The only way they can put up hotels is by them landing on their own properties and putting 4 houses on them first. But if the difficulty is set to High Skill they should be able to get houses and hotels in no time. I also suggest playing Industrialist Mode or Tycoon Mode as Industrialist Mode has 9 rounds and Tycoon Mode has 12 rounds which will give the CPU more time to get hotels.
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Credits go to Bishop24 who wrote an entire achievement guide for this game on xbox360achievements.org (
http://www.xbox360achievements.org/game/monopoly/guide/). His solution for this achievement is very good, and I wanted to share it here.