Hey Ali, attic conversions are a great way to add living space, but it's not always a simple job. Although there are some structural limitations, adding a dormer to a space that's already heated can usually be accomplished with an over-the-counter building permit (STFI). If you're converting unconditioned attic space to heated space then you'll have to go through plan review. You'll need to provide a complete drawing package including floorplans, exterior elevations (if making any alterations to the outside), section details, structural calculations, and energy code information. It's a big job to tackle yourself, but certainly possible if you have the time and patience.
A couple factors to keep in mind...when converting from heated to unheated, you'll have to insulate the roof. Depending on the era of your house, many attics were framed with 2x6 or even 2x4 members, which doesn't allow for adequate space for the insulation depth required by the energy code. So you may need to furr down, which would impact your headroom. Floor members often need to be beefed up as well, since they were originally intended to only support the ceiling. Access is another tricky issue. If you already have a stair that goes up to the attic, you can usually leave it there even if it's non-conforming. But if you have just a ceiling hatch or a pull-down ladder you'll need to build a conforming staircase, which can have a major spatial impact on your main level living spaces.
Hope that helps. If you want to talk to a builder or designer I can certainly recommend some folks. I know a lot of each!