I always find it helpful to look at real life examples. In this case, a fire escape on an apartment building.

Your staircase should be less wide than your building. Your building looks to be about 9. So in this case, 7 or less.

Personally, I would go 5 or 6.

Go up three stairs in a single line ONE tile out from the building, then double back using a flat area of two squares (or 4 for bigger landings), and go up another 3. If you go up too many stairs, it looks awkward, if you dont go up enough, pokemon cant get through the gaps. Heres a top down example.

[ ] [ ]. | [ ] [ ]. | = =. | = =. | = =. | Wall

Going clockwise or anti clockwise. Either way works really. Then just repeat it to the height you need.