With Blocky Man, the method I used to do this was very simple. I named the map files:
etc...(not exactly, but something like that)
Than I hacked the code to make the levels play in order.
Now I'm going to code it so a group of levels will be packaged into a "world". This will allow people who make their own maps to group their levels. After all, I'm hoping to make this game something people will want to create maps for.