Heya,
I like the theme and storytelling quite a lot. There's a couple of issues I see though:
Careful with your horizontal and vertical line. It's especially noticeable in 1-point-perspective when they are off, as they should be perfectly parallel instead.
The backwall is incorrect. When trying to find the plane of the back wall (indicated by the blue arrows) you'll find that the size of the plane would be about what I painted in orange. I've also drawn in where your backwall would sit, if it were the size you drew it.
So basically, your room under the walkway would be inset into the backwall, but the beams on top indicate otherwise.
A way to avoid this is to follow the convergent, horizontal or vertical lines from points in space where the position is known (for example the corner or edges of the room.