You must make your custom files on Noggit or you can get your maps modified parsed to Cata, MoP or WoD and convert this to Legion.
If you use the ADT Converter and you use "-l" this convert to Legion, but this can give error because the wdts, wdl and tex fails and the water dissapear. For fix this, you must parse your maps from Wotlk to Cata/MoP/WoD with this tool ADT Converter
After you must put on the data folder yours maps modified and you must make click in the .bat file, this parse alls files to WoD (Cata and mop too). Now you must download the script file and .bat modified for me, this files Adt Converter to Legion
You must unrar, after you must edit the bat file and you find:
010editor "%%i" -script:"PATH\ADT-Legion-Conversion.1sc" "%%i" -nowarnings -noui
Now you must edit the PATH for your path folder of script file, after you save this.
After you must copy your ADTs files only from Cata/MoP/WoD to ADT folder and now you must click in the .bat. When this program closed, you must get the ADTs and put on the path folder patch (World/Maps/example/example.adt) in your World of Warcraft root folder.
Et voila, your maps it's working. (Delete WDT, WDL, TEX files for this work)
Like the post if you like it! and sorry for my english.
Credits: Luzifix (Adt Converter), Arektor (Script 010editor of Wod to Legion), Me, Darkkang for make the tutorial and the .bat file and testing this.