This is just my personal opinion but I like the least amount possible, for the sake of looks and the amount of lift
 
       The purpose of Dihedral is for stability.
  There's no reason to add any more than necessary.  Too much dihedral lowers the amount of lift.  It's a trade off.  Compromise.
   That's how dihedral works.  The higher, more angled wing lifts less than the lower, flatter wing and that levels it out.  The flatter wing lifts more, therefore picks up the low side.  In the case of contest planes, they fly regardless of the wind speed, or wind gust speed, so they use a lot more dihedral than I like just in case of a big gust of wind.
    I only fly in fairly still air.  If it's windy or gusty, I just don't fly.  I don't need the high level of stability that contest fliers might need on contest day.  Some indoor planes have very little dihedral because they have very little wind.  I have flown outdoor planes with almost no dihedral at all.

  If it's possible, maybe you could test glide with the least amount and add only that which you need to get a stable flight.  As a basic rule of thumb, if your wingtips are above the thrust line, or center line, you should be fine in stable air.  One way to test this without flying it is to lay the wing tips on you fingertips and see if it will balance fore and aft.  If its not a swept wing aircraft, you should be able to hold it without it falling off your fingers.  This is just a guideline, not a hard rule.  It will give you some idea where to start.

  Again, this is only my personal opinion.  This is only what I do, it may or may not work as well for you.  Most folks adjust these ideas to suit where they fly, and the conditions they fly in.  How windy is it where you live? That is the deciding factor.  More wind, more dihedral.

   Your english is fine. No worries. I hope this translates for you well.  I wish you the best of luck and please let us know how it turns out for you.

I believe it's the same.  For the low wing aircraft the  ROT (Rule Of Thumb) is to have the wingtip at or just above the bottom edge of the cockpit.  You can achieve that when you build the gull wing add the dihedral to the upsweep of the outter panels of the wing.