Buy whatever buildings you can find, and if you're strugling, start redecorating houses with better furniture.
Definitely make sure you've bought:
- Graveyard Mansion (Bowerstone Cemetery - you will have to complete the 'Love Hurts' quest to unlock this building for purchase)
- Reaver's Mansion (Bloodstone)
- Fairfax Castle (Fairfax gardens)
- Brightwood Tower (Brightwood)
I had quite a bit of trouble with this achievement, even after buying every building I could find, including the graveyard mansion, bloodstone mansion, fairfax castle and brightwood tower.
It may have been the terrible economy in most towns due to my regular thieving and murderous rampages, but the way I nudged my real estate worth over 2.5 million was to redecorate some of my properties with the most expensive furnitures I could buy. Considering the number of houses that can be redecorated, this achievement becomes easy with a few trips to the furniture shop.
Obviously this assumes you can afford things in the first place, but aquiring money isn't very difficult. Purchasing shops and buildings (provided you rent them wherever possible) will earn you money every five minutes, even when you aren't playing (although this will only be 10% of what you would earn if you were in game) and if you don't mind being corrupt, you can increase prices and rent by as much as an extra 100%. If you don't mind cheating a bit either, you can change your xbox system clock.
To do this, ensure you're disconnected from xbox live (live automatically sets your clock to the correct time) and head to 'System Settings' in the 'My Xbox' row of the dashboard, select 'Console Settings' and move down to 'Clock'. Hit 'A' and you can set the 'Date and Time' (this is where you must be disconnected from xbox live, or the option will be unavailable). Here you can simply set the date as far forward as your console will allow, which for me was the 31st December 2025. Return to Fable II, and within a few minutes, you should have a nice lump of cash. Save the game and you can carry on as usual. If you want to earn even more money, set the clock all the way back (mine went to the 1st January 2005), enter Fable, save your game, then put the clock forward as far as possible, and return to Fable, and you should instantly gain 20 years worth of earnings. Nice! With most of the real estate, this method bagged me over 2mil in one go.
Then simply ensure you've bought as many buildings as you can find, and provided your economies are stable, you should get 100G. Remember that if you're struggling to reach 2.5 mil real estate, upgrading furniture is an easy way to do it. I only had to partly redecorate three houses (partly due to the limited availability of some furniture items) before the achievement popped up. Hopefully you'll have it in no time too.