Are you a sole proprietorship or a 1 person LLC? If so, don t charge yourself rent - just take the deduction for a home office expense.If you are a corporation and you want to record the expense in your corporate accounts, find out what some nearby offices are leasing out for and divide that by the square footage. Use the price/sq. foot calculation to determine what the fair market value is for the part of the home you use.
If it a rented you need to see how much you pay per square foot. then measure the room in the home multiply that. If its not rented check you area what is the price for a square foot. measure the room and again multiply and that the rent for the room