I don't know if anybody has already offered this idea but i would share it with other people.
This Level-up system is not based on minerals, it is based on points.
It is only for all characters and not for one alone!
1)First you have to make a points-boardage with "own-points" for all players(not the computer players). You should call it "of NUMBERExp/LevelNUMBER". At the first NUMBER you should write the needed experience for the next Level and at the second NUMBER place you should write your actual Level. So, if you need 1000 EXP and you're actually at the first Level, then it will look like this:
"of 1000 Exp/Level 1"
2)Then you make a trigger for each Level.
As condition for the second level you need to write "if Player # has 1000 own points" and a switch witch you call "Level-Up". As action you have to change the points-board to "of NUMBER Exp/Level 2" where NUMBER is the Number to the next Level. You have also to set the switch "Level-Up". Don't use "Keep Trigger"!
Go on like this with all next Levels.If you have 30 Levels, you have to create 30 Triggers.
3)Then you have to create a Trigger for all Players. As condition you have to write "if Switch Level-up is ON". As action you have to write "show text message" with a useful text like "Level-Up!". As second action you have to set the switch "Level-up" OFF. And as last trigger you have to write "Keep Trigger".
If you don't see the message you have to insert "Wait 1 ms" between the first and the second action.
4)And at least you have to create with SCTrigger some trigger for all players, where you get points for each kill!
If it won't work, you can ask me if you want.