According to Harry Muscle :
I'm starting to design an insulated shed I want to build later this
year. I'm pretty decent with woodworking (not a pro, but I can build
things no problem), but I've never build a shed before, so I have a
couple of questions. Since I want to use this shed for projects
throughout the year, I need to insulate it since I want to heat it in
the winter (I'm in Ontario, Canada). I still haven't finalized the
size, but it's gonna be either 10x15 feet or 12x12 probably. My first
question is to do with the roof ... do I need an attic in such a shed?
I know the point of an attic in a house is to keep the roof the same
temperature as the outside to prevent snow from melting and refreezing
on the roof ... is that the only point of an attic in an insulated
building? Do I need this on a smaller roof? If anyone could shed some
light on how I should be designing and insulating the roof part of this
shed, that will help.

I'm in Ontario too (Ottawa).

If you plan on continuous heating, even if set low, I'd recommend
an attic. Insulation, vapor barrier, and drywall. Drywall is cheap.
Properly venting insulated cathedral ceilings (you MUST insulate) is
a PITA. My grandfather's cathedral ceiling on the cottage wasn't
vented and rotted out.

Consider making the walls 9 or 10' instead of 8'. Better for a
workshop. Cathedral ceiling with trusses might as well be attic
w.r.t. storage.

For storage, ensure you have a good sized hatch.

I suggest a metal roof with a high pitch (ie: 1:1). A bit
more expensive than asphalt shingles, but longer lived and
less trouble, and the pitch tends to clear the snow
automatically. Metal roofing is easy to get. Even the
Home/Pro Hardware guys can order it.

On a shed this small, make your own trusses - 2' centers.

For exterior treatment of the walls, if you're not terribly
fussy, I'd go with vinyl siding. The shed I built did, and
it was easy and inexpensive, and pretty durable.

Think windows, lots of 'em. Make your own. Get the SO to
make drapes out of "remaindered" towels ;-)

At least match building code for the floor joist size/spacing.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.