An up to date method to set lobby teams to in game teams that also adjusts pre placed units/buildings in you map to assign them to the correct player.
Just copy and paste the triggers into your own map and adjust them accordingly. Currently set for a 4v4 map but can easily be edited to more or less.
This is the same triggers used in my map, Legion TD 2.
Things to set in your map options:
Player Properties -> start locations must be set (NOT random)
Player Properties -> players must be set to Users
Player Properties -> Team Placement (Basic) -> set start locations to players. Start location 1 belonging to player 1.
Player Properties -> Team Placement (Basic) -> make sure NOT to link any allies here. allies/enemies must be set by triggers.
Player Properties -> Team Placement (Advanced) -> make sure not to link any allies/enemies here.
Game Variants -> Locked alliances on.