Despite the stereotype, procedurally generated systems can be impossibly hard to design enjoyable formats for. Honestly I tried multiple times to create a procedurally generated system to no avail, and i have some decent experience in the software. Making random content still be fun can be surprisingly difficult, and making that content last requires a lot of testing and very specific formulas. Would recommend hand crafting a few small levels that are really good before going out to try procedurally generated content.
If you'd like to keep going anyways, the main thing to understand is that your game needs structure around the randomness. If you want to try developing in a "module" approach, my advice would be to create a "room generator" object with no sprite. This object will draw sprites, set walls, and summon objects to the tune of preset variables. Pre-set in the create event the generated room sized, how many rooms are allowed to spawn, how many enemies per room, and any other system your game needs (start small obviously). Then generate all of your rooms (still in the create event), making sure the rooms don't intersect
