This is a cumulative ach (i.e. you dont need to build 100 houses in one game) a quick way I found to get this was play a custom rules game with minimum tax and maximum free parking, Go salary and starting money, also set the ammount of houses the bank holds to maximum.
Start the game with just you and a 2nd controller then progresivly win all the properties by auction for M1. Once you have all properties of the same colour you can build houses, you can build houses then save then go back to "Build & Mortgage" remove all houses, then re-build them again keep doing this until the ach pops up.
If you have all the properties (22 in total) with 4 houses on each you can build 88 houses every time you do this process.
Hope this helps!
NB: This will also work for the "Subdivision" ach