Hello, 

I open a scenario map, originaly from COH3 in essence editor, make changes, add players, resize the map etc.

in the end i want to complete the map, build it to be able to test it, eventually publish it, but when i use build mod thing in editor, it only make a 20kB.sga file (not something like 10MB sga file)
So it is not possible to test it, play it, nothing :(

Thanks for possible answer :)

You need to create a new version of your map by creating a, what is called a empty extension ,

See the guide here how to create a new empty extension and then copy the map into through this by giving it the name you wish and then you have two separate copies of your map

How to duplicate your map into a new mod https://youtu.be/u2PaUhstZsY?t=391