Realtor Flipping a home. How much concessions for windows and roof?

First time investor starting out with a owner occupied duplex. It's a 4 bd main house and 2 bd apartment above the garage.
1. The seller is a real estate agent who purchased 3 months ago, did some work and selling.
2. The 2 bd apartment windows are old and will need to replace soon
3. Roof age is unknown- seller doesn't know. We suspect it might very old.
Selling- $380k
Mortgage- $2800
Apartment rental $1200

How much reduction should i ask for
the roof and windows?