Stairs take up more space than you might think. You need a landing at the top, you can't just go through a door half way up like you have shown. You also need space at the bottom that is clear of intrusions such as door swings.
If the building has more than 2 floors, you need to think about how you get to the second flight. Depending on the uses of the building, single domestic dwelling, shared stair serving more than one unit, commercial, all effect the dimensions of the staircase. You also need to consider fire and sound separation.
There is a lot more to this building designing malarky that people give us credit for. Seriously, you need to get some help before you go too far down the line with a project that you think will make you some money.