Wesley L., I do add on flips a lot right now. It makes sense in the areas where price per sqft is $500+, but areas that are less than that seem to be more work than the pay off is worth.
Here is my rule of thumb for you.
Your cost to build at the very low end is going to be $100 per sqft new construction. Your cost for rehabbing the existing house is going to be $50 per sqft.
Here is the math on your example 1100 sqft = $60k remodel + 1000 sqft new construction = $100k, total rehab on this project will run $160K. Not including your plans and permits.
Then of course you have fixed costs, holding costs, realtor fees etc.
Upon quick calculation it looks like you could make 90k if you exit at 600, however if you exit at 500, you make zero. In fact you lose 10k. This is a minimum of 6 months work. Lot of work with not enough pay, for me.
PS many of these smaller homes have only 1 car garages, if its a single car garage and you are adding another car space there is no value added for that extra sqft you add to the garage. Usually a 2000 sqft house has a 2 car garage.