An outbuilding is where most builders quietly drop their standards, because nobody is going to look closely at a garage slab. We pour them to the same spec as a house floor, which costs a little more on day one and saves a cracked, heaved mess a decade later.
Matching the house
Siding, roofing and trim get matched to the main house, and the roof pitch is set to echo it. A detached garage that reads as part of the property is worth considerably more than one that reads as a shed.
