They covered about everything, but you also have the extruded sides of the cinder blocks running the wrong direction. They should run parallel to the holes.
For this assignment we have to create a building using modular assets that snap together. Earlier this year I made a game concept titled Spicy Jam so will be recreating one of the environments (the Subway/underground) for this project. I didn't get to make concept art so got advice to pick an existing train station to base…
What the best (or easy) way to inflate a copy of a lowpoly mesh for use as a cage when baking normal maps? Kinda like how extrude pushes away from each face...like a ballooning affect
extruding an edge will work, can't say off top of my head if it will have planes on both sides. obviously he didn't delete back faces as you can see between legs
Horns might even be better left as separate subtools unless you wanted a perfectly blended transition. Depending on how clean the extrude is and how long the horns are, slice curve is another option.
Does it appear in the outliner? If so try giving it a new material. As for the flipped faces looks like you extruded without taking the face's normal direction in consideration, that's probably why they appear flipped.