You DO have a building permit right??? If not, your homeowners insurance might not cover you when the roof flops. If you don't do this right, the only insurance your family will get is your life insurance. Anyway, what you are looking at is basically what bc said. If you want to remove the ceiling joists (collar ties) then you need to support the roof ridge so that the weight of the roof doesn't make the walls spread out and have the whole room collapse on you. You could install a "ridge beam". This would be a heavy beam put under the peak of the roof, posted up on either end (inside the walls). This would then hold up your roof. You would need to make sure the connections between the rafters and the ridge and wall top plates were strong and maybe reinforced with metal connectors. You would also need to make sure that the beam posts had adequate bearing support, ie: foundation and/or footings. You would also need to make sure that your rafters were properly insulated, vented through the soffits and ridge vent, and vapor barriered. see: http://www.jlconline.com/jlc/archive/energy/cath_ceiling/index.html You also want to install a top quality fan, like a casablanca, that is strong enough for this size room, that would help equalize the heat/cooling top to bottom. Otherwise the room won't be comfortable. Plan the electrical ahead of time and also put some track lights up there too. Have fun, do it right and get a permit and some engineering.