Roof repairs

You can really do it yourself with 2 workers if you speak basic Spanish. You just clean roof, swab it with the sealer, swab it again, put fabric on it, swab it twice more and you are done. This is for flat roofs. I did my roof a few years ago like this and spent under 4,000 pesos.

Fabric is a polyester type and comes in rolls about 1 meter by 50 meters or more. It protects the roof as it is a complete layer of something. To keep you home cooler and make the roof last longer use the white colored sealer and not the red stuff that draws the heat.

What kind of pitch is needed. I have only a 20mm pitch on 5 meters

Polyester? Are you sure it's not fiberglass? In all the roofing jobs I've been involved with, we used fiberglass.
Example here.

My painter/roofer refers to it as "membrana" i.e. membrane and it looked like woven fiberglass to me.

It could very well be fiberglass but it is soft and seemed like polyester or a very durable felt.

Just did our two small flat roofs using Fester products...as recommended by "newinajijic" (John)...can't believe I just typed that!
Anyway, the guys who did the work were very impressed with the products and said it is the best stuff they've worked with in a long time.
It's a line of products made to work with one another and we started from scratch by power washing the roof to within an inch of its life...then sealer, then acriton 10 year, then membrane (reinforced flexible polyester fibre) then more acrition 10 year. The membrane is applied before the first coat of acriton dries and then the second coat of acriton immediately thereafter.
http://www.fester.com.mx
We didn't have any cracks to start with but if you did, you could use either of the two kinds of filler (resanador) that they have...in cartridge or pail.
The slope to the drains was OK but they checked with a ball to make sure...said any low lying areas could be built up with membrane and acriton until the final membrane "finished" it. Oh yeah, overlap the membrane by starting at the drains (lowest point) and working to the highest point...and make sure you go up the parapet about 4 inches too.
I asked a lot of questions and did a lot of reading before starting this project 'cuz I'm curious.
I'll still check every year but I think we're good for at least another 7 years.

Now also note that I had leaks after I did my roof..... BUT it wasn't from the roof so also be sure to check for cracks and holes in window tracts and spaces where water can run down walls, etc. These are other ways for water to get into your home even with a new roof.