You need to have a pitch somehow. Basically your options are either slope to a drain(s) in the interior or slope to the edge. If you don't want an interior drain, it sounds like you're going to be going to the edge—e.g. gutters or scuppers.
If you do use a drain or scuppers, you should also consider what would happen if they clog. You don't want to set yourself up for a situation where more standing water can accumulate than the structure can safely hold. If the parapet is solid, you could potentially get a lot of water up there over time. Every inch of standing water adds about 5 psf, which could add up quickly. Also, standing water has a tendency to "pond" — cause deflection in the middle of the roof, which draws more water to that spot, which causes more deflection... etc. etc.
2 LAYERS ASPHALT TO CP144
with SOLAR REFLECTIVE PAINT
on [10?]mm PEARLDECK ([.025/.023])
ON @@@@@ SC3 Joists
AT #00 CENTRES
@@ RRING [PIECES?] [10?/TO?] @@@ 1-30
CP144 is a standards document describing roofing requirements. (It's been superseded.)
Based on some cursory research, it doesn't looks like Pearldeck comes in 10mm thicknesses, so I'm not sure what that number might be.
SC3 is a European strength rating for joists that has been replaced by a different rating system. (According to the link, SC3 is roughly equivalent to C16)
I'd bet that the last line is "100 CENTRES" with 100 being cm, which seems to be a common spacing for joists.
Pearldeck is hard to find, but based on these two sources:
http://www.woodgreentimber.com/Roofing-Materials-Wood-Green-Potters-Bar.php
http://www.euroken.net/supplies/products.html
It looks like it's an insulation board for roofing.
As to whether or not it's a good roof, cold, hot, or anything else, I have absolutely no idea, and it will largely depend on your local climate. Maybe an expert can add something to this answer, or maybe my translation will let you ask someone you know.
Lastly, not only am I not a professional, but I'm also American (I'm not familiar with common European building measurements/practices), so any or all of this might be completely wrong. This is all based on deduction and Google ;-) So feel free to edit whatever is obviously wrong.
I hope that helps!
Best Answer
There are several ways to do this but given that the building is small, not in the Far East, and obviously not an expensive architecture demonstration, the builder probably simulated carved rafters by adding carved wedges or stacked wedges to standard rafter beams.
Given the apparent age of the building, the roof cladding is probably 1" boards fastened horizontally, which would naturally follow the curvature of the modified beams. The builder could have chosen from 1" x 8" to 1" x 4" with the narrower boards being more work but giving a smoother curve.
If you were building this today you would probably want to use plywood cladding, so you would put it all together with strong fasteners like deck screws and just force the plywood into the desired shape.