Creating an offer for a home with a detached garage w/ basement

[Hailee Segura]

I am looking at a potential deal that the seller is including a detached garage with a basement in the homes total square footage. When gauging an offer price, would you include the square footage of the detached garage into the homes total square footage or keep them completely separate? 

When turning this into a buy and hold rental, what would you do with this detached garage with a basement? Turn it into a second home?

Thanks!