The roof deck is the section of the roof onto which everything else is placed. As such it needs to be strong enough to hold the weight and durable enough to cope with some give. Depending on the type of roof you are having installed you will need to decide on the type of roof decking you use and the roofing contractor you propose to use will be able to help you make the best decision on this. There are, though, essentially two different types of wooden roof decking. There is plywood roof decking or tongue and groove roof decking.
As mentioned the type of roof decking you need will be dependent on the roof you intend to place over it. As a general rule, though, plywood roof decking is much more rigid but does not allow very much in the way of roof ventilation because it consists of solid pieces of wood with very little room for air to move in or out of the attic. If you intend to use plywood roof decking you will have to find a way to ensure that you are getting adequate roof ventilation or you should change the type of roof decking you intend to use because good roof ventilation is absolutely essential to the integrity of the whole of the roof and, therefore, the rest of your house.
Tongue and groove decking is often made of stronger wood than plywood and does allow for good ventilation systems as long as it is fitted by somebody who knows what they are doing. Tongue and groove roof decking should be fitted carefully and properly to ensure that it is strong enough to take the weight required when the job is completed. Again, the only way to ensure this happens is by using a qualified professional.
The roof decking you choose can have a strong influence on a number of further decisions you will need to make regarding your roof, and you will in particular need to consider the effect it will have on your proposed method of roof ventilation. Effective roof ventilation requires an intake or air into the attic and the expulsion of air from the attic so by picking solid roof decking you are essentially making this job a little harder. Let us know if you need help determining the best, informed decision you can make to avoid making things more difficult in the future.