Welcome to BYC. Where, in general, are you? Climate matters, especially when it comes to housing.
If you have an area subject to a good deal of frost heave you'll want a sound foundation so that your coop doesn't shift and settle.
If you have very soft soil you'll also want to take care to set your coop solidly so it doesn't settle.
Settling is to be avoided because it will cause doors and windows to jam and *could* create openings in your anti-predator perimeter.
If you have a lot of wood-destroying insects you'll want concrete to keep wood clear of the ground and/or to use ground-contact-rated treated wood.
If none of these factors are a major issue for you then you could set your coop wood directly on the ground, maybe laying sturdier beams down to establish a level base to work from.
How are wooden sheds normally set up in your area? That's often a good guide for chicken coops in the region.