My understanding for the business use of home for childcare the equation is:

square footage of home / square footage used for business X 24 / # hours you are open X 365/#days a year you operate = % of expense you can write off.

So for example - if your home is 2400 square feet and you use 1000 of it for daycare during business hours, you are open 10 hours a day lets say with 30 minutes for prep before and after on average so 11 hours total, and you are open 240 days a year cause you take 2 weeks vacation and are closed for 10 stat holidays.

1000/2400 x 11/24 x 240/365 = 12.5 % of any shared expenses ... so $625 of your roof would be able to be written off as a 'business use of home - repair and maintenance' .