I really like this! The procedures are fun and the oracle table looks like it would be fun to use.
I think some minor tweaks could make it more user friendly:
I had to read the Ruin Engine procedure twice before I understood it. I think putting a little label explaining that L0 rolled a 5, then a 3, then a 2, then a 6 would make the procedure much clearer.
The d100 to determine stairs is confusing to me, I think an example of how exactly the roll relates to the map would help.
I'm also not sure what "set the probability that the objective will be found by the desired difficulty of the scenario" means. What does it mean that an objective has a 30% chance of being found and how does this interact with or relate to the PCs actions?
I have read Roadside Picnic, but don't remember what "mosquito mange" is, I have not read the other referenced works. I think these references may frustrate more Wardens than they inspire.