I understood your question in regards to the insulation. I asked about the use of the room (bear with me I'm not up on the National Building Code) but most building codes have a requirement for an Emergency Egress and Rescue Opening for bedrooms. This is a certain sized window so that firefighters can make entry in an attempt to rescue trapped occupants. Sometimes people are not aware of other code requirements when planning a project, or asking a particular question. I try to answer questions to the best of my ability, but also to ask questions that may pertain to other aspects of the project. Make sense?
Insulation application can be based upon whether you have soffit and ridge vents or not. If you have a vented attic space (soffit & ridge vents) I have used insulation baffles installed from the soffit to the ridge vent and installed closed cell spray foam insulation in the rafter bays. The insulation baffle allows ventilation under the roof deck and provides approximately an R-15 for your existing 2x4 rafters. Of course you can pad out the rafters and apply more insulation. You could also apply rigid insulation board to the existing roof deck (sheathing) to increase your insulation. Of course this would require removal of the shingles/roof covering to accomplish. If you current roofing is in good condition this would be a costly endeavor, if it needs replacing now would be the time to do it.
I would highly recommend checking with your local building department to determine exactly what the code requirements are for the type of project your are planning. Again, I have never done work in Canada and I am not familiar with the National Building Code so some of my advise may be incorrect for your code requirements. Here is a link for Building Standards in Regina
Hope this helps ....