John Sayers' Recording Studio Design Forum

Hey all, and thanks for this fantastic resource!

I have been hunting for spaces to build a mix room in for a few years now, and have never quite found the perfect space. I only have $5000 to spend, so need to find a space with a lot of the requirements inherently in the building. (can get more by saving more, but I am ready to go with this)

I have just found a space which may just cut it. It is in a concrete double story building, on the bottom floor. The walls, floor and ceiling are all concrete.
There is a train station nearby, so soundproofing is a must.

This will be used to compose in. No recording. I write music for theatre and dance, and also write break beats, techno etc etc.
I have PMC TB2's, and will be acoustically treating the space. One day I dream of adding the TLE1 sub.
I still have much to learn although have read forums for years so not an absolute beginner.

The good thing about this space is that 5 of the spaces sides are concrete. The last side is a roller door, however there is enough space to build a wall with door in it 1 metre from the roller door. As I am not recording, I assume the concrete will be able to stop enough sound coming in/out.

There is also a heating cooling unit already installed! win.

The space is large, I do not have the dimensions yet, but it was at least 25 sq metres of floor, and the ceiling would be 5 metres up as well. It may be a bit cubeish, but with that amount of space I can easily move the wall I need to build in to improve the ratio.

However!
The first factor so far that makes this space tricky, is the stairwell.

Well, more, the underside of the the stairs which head up to the 2nd level. Again, it is all concrete, but I am wondering what this may do to especially the low freqs. See image.

My question which I would greatly value responses on,
Is what sort of problems might I be looking at based on the information I have been able to give?
I am assuming
1. Budget too low... (always is..)
2. Symmetry - lack of...

EDIT: guys I should add, that your advice on the protruding stair well, and its effect on the acoustics, is something that will most likely affect my decision to rent this space or not. I do know that it will do funny things to the low end. I don't have experience to know if it is worth a risk, or clearly unusable. I know measurement is the key but I can't measure a place i haven't rented.

Thanking you very much in advance for taking the time to assist me!
cheerio,
Evan

Sketchup not to scale. Yet.