We also bought the house with an unpermitted addition (large bedroom and bathroom).

You could offer to pay for a few months at a storage unit or give them a discount on rent to supplement them loosing the garage. 

Our gut rehab added 2 full bathrooms and a short term rental unit in the basement.

If so, do you offer a discount if the tenant maintains or just put it in the least that it is there responsibility regardless? 

I converted a garage and installed a kitchen sink, bathroom sink, and toilet.

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Purchase price: $45,000 Cash invested: $65,000 This is a Single Family property that we acquired out of an online auction, added a new bathroom and a few other minor updates, the majority of the home had just been updated in recent years.

We replaced the windows, floors, new paint, new bathroom and several other updates throughout.

The owner had the Master bedroom and bathroom, I would have gotten the smaller bedroom for $750/month plus utilities, and he was renting out the basement for $850/month plus utilities.You could even look out to western Howard County in the Fulton/Maple Lawn area.

Principal is easy to calculate, but there are many factors that determine your interest cost/rate (LTV, Credit score, discount points/credits, etc).