Here is my plan (not that I would use one, but here goes):
1) Decide on depth of roof required - most are 4" or 6" (in old money) so 100mm or 150mm. (those shallow ones look nice but are less practical - see bottom comments)
2) Cut 2 pairs of sides.
I pair will be 460mm + twice the wood thickness + clearance for fitting the roof.
The second pair will be 460mm + clearance for fitting the roof.
3) Glue and screw them together so they are square.
4) Make and fit battens to sit the roof on the hive box (do it now and no gaps need be left between these battens and the box top). Use an existing hive box to make sure all is square - side clearances are the same each side!
5) Cut 2 isosceles triangle pieces with the base being the length of the roof (460mm + twice wood thickness + clearance) and the perpendicular height being that which gives a suitable pitch for the roof.
6) Glue and screw these parts in place.
7) Make a triangular section bar (at the same angle as the apex of the roof) of length 460mm + clearance and fit between the two apices(?). 2 pieces of wood bevelled at the correct angle and fixed back-to-back may be an easier method of making the ridge bar).
8) Decide on overhang at front, rear and sides of your roof and cut roof panels to appropriate sizes, in appropriate thickness, and material of your choice.
9) Fit roof panels and cover them with a waterproof protective material - aluminium, galvanised steel, asphalt sheet....
10) Make and fit a ridge protector if required.
11) Fit insulation inside roof if required (see below).
12) Fit at least one bee escape to avoid trapping bees in the roof-space and/or make ventilation holes and cover with mesh (to prevent access by wasps, etc. but allow hot air and moisture to escape).
13) Decorate to one's own design.
Lots of modifications are possible - you might want to bevel the sides at the same angle as the roof pitch, in which case the finished outside dimension will be the chosen roof depth (basically need two different widths of timber). You may wish to add drip rails, mini-guttering or other aesthetics.
The order of the plans can be changed to suit your particular method of construction.
You may wish to make the front and back as a one-piece part - if you do, make them fixed together, so they are identical, if you are not a regular DIYer - or you may wish to make fancier joinery joints (mortice and tenon. or dovetail. or lap joints - your choice and in that case the lengths will need to be changed, allowing for cutting off 'horns' if relevant.
Basically, you can take a square brood or super and simply build onto that, piece by piece, until it is finished. No sweat, no plans needed, only a basic design sheet.
Lastly, might I ask: why?
The flat National roof is fab for turning upside down, when removed and laid on the ground, and used for standing hive sections on it as they are removed. A pitched roof is NBG for that. Flat roofs are simple, these are more complicated because they are fancy. The bees will not notice the difference one jot. The roof is basically an aerofoil shape and may try to lift if the wind direction and speed happen to be favourable (a flat roof can lift as well). It will be heavier than an equivalent flat foof.
I use a flat sheet of expanded polystyrene as extra insulation for the winter months - a deep roof easily allows that to be added and still have ample roof overlap with the box it is covering.
But it your choice, good job everyone is not alike.
PS - if I have missed a trick oleas feel free to put me right - especially the video king!