Procgen

How does ivan generate it's maps ?

I believe they're carved out of digital suffering.

What do you mean? The world map, or a dungeon map?

Dungeon's ie GC UT

Id imagine it either connects some prefab rooms ie UT'S diamond shaped room GC'S Merka's shop using tunnels of diferent size's

I haven't really studied the level generation alogrithm much, but AFAIK it first tries to place all the prefab rooms for the level and force-aborts if unable to do so, then places some random rooms and generates all doors, then connects the doors and other square with required attachement by tunnels dug in the shortest way that doesn't intersect any room. There is no code to create wider tunnels - they happen randomly when two tunnels are created next to each other.

Have a go with this build-a-roguelike tutorial. It's in Python, but same idea: http://rogueliketutorials.com/libtcod/3