If you are going to lower the ground level on the inside of your foundation, you will go below the level of the footings, and undermining the footing is a BAD thing. So, then you have to figure out how to make your foundation DEEPER while the house is still sitting there.
This is EXPENSIVE.
The best way to increase the size of your home is to go to True Value and bring home a post hole digger and a 4x4. Stick it in your front yard and put a great big piece of plywood on it, and paint it with the words "Fer Sail, y'all!"