a local architect.

ABSOLUTELY!

First if your going to do this RIGHT you need to insulate the roof and
add ventilation between the space and roof decking, rather than
concern yourself with the attic floor. lack of ventilation can ruin
your roof fast

you will need air conditioning, and should do that with a larger effort
to do the entire home. true you could put a big hugger window unit up
there but they are costly to operate and dont add value to your house.
for resale reasons air conditioning is becoming standard today, unless
you live in the artic.

if you dont have a dormer this might be something to consider, it adds
light and space.

its definetely possible the architect.can give you a iidea of total
costs