Entrance Door and Wall

Hello, The apartment used to be together with the lower floor, but a drywall (gypsum board) wall was built at the entrance to the staircase that leads up to my floor, separating it into two units, B1 and B2. The problem is that this wall is very thin and basic. When you look from the other side, there is a gap between it and the staircase and you can see the upper floor. In other words, the area between the wall and the stairs leading to my floor is open. The door that was installed also opens outward and is a very poor-quality door. Therefore, I would like a better and more secure wall and door to be installed here. I look forward to receiving your price quotes.