How much do you take off the property value of a house for these problems?

I am a college student I inherited a house from my mother who was not able to take great care of it. I inspected the house (which is made of almost entirely wood) and found that a lot of the siding has wood rot. I called an exterminator to the house and there wasn't any termites but their were rats in the attic. I have no money to pay anyone to remove them and don't have great credit. I have no idea how to fix these problems on my own so I want to sell the house as is but need to know how much I should take off for these repairs. I live in Merritt island FL the roof of the house is almost 18 years old and it does not have an ac system.
Added (1). I do not want to list it with a realtor if I can help it. I've talked to one before and if I list it with a realtor I might not get enough money from it to pay what is owed on the mortgage.

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