I'm not sure if this was cancelled or not but here's my idea:
There would be a couple preset sets of tiles, because if there's a whole lot of tiles it would be hard on the game.
if it's possible the people could make custom tilesets. in the code would be <tileset></tileset> you could enter 1 for preset 1 etc. imagine you wanted spikes, fire, water drain and water tap it would put down <tileset>spikes=w water tap=! water drain=? fire=m.</tileset>
terrain, door and starting position would always be added.

Not sure what use this would have.

AFAIK, the amount of codes used for the tiles doesn't matter, as the game has to load it all no matter what,even if they don't have a letter or symbol attached.

well, at least i tried. i should start learning programing language

If you do, Start with Python. It's the easiest IMO. You can also learn others off of Python

^This.
Once you've got some object oriented stuff, you could transition into c++, which is one of the most widely used languages.

i barely know what a programming language is. time to do some research!