On the positive side, an attic is an interesting space to use. There are usually several options available to you in terms of how you will use the space. You can either work with the slope of the roof or provide additional headroom with a dormer. There is really no tradeoff of space with other parts of the house because the attic is generally under-utilized or not used at all. Because you already have a roof and exterior walls, it is relatively inexpensive to build interior walls to partition the space.
On the negative side, you will probably need to install a sub-floor – these are not ordinarily included by builders. The pitch of the roof can present some real challenges in terms of how you can use the space. If the roof is steeply pitched, you might discover that there is a very limited space in the center with enough headroom for use. Your options will be to try to find creative ways to use the “dead space” on each side or to build dormers to extend the space. In addition, access to utilities could be difficult, ventilation might be a concern, and building codes might require egress directly to the outside.