It depends on what type of bass trap you want to make, there's a few different kinds that people use. The first is essentially a panel, much like a broadband absorber, but with much thicker insulation. Usually anywhere from 4-8 inches thick of as apposed to the 2in thick panels of a broadband. That extra density from the added insulation allows the absorption of lower frequencies. The air gap behind the panel is kind of like a small resonance chamber and a lot of people believe because of that, they work better than the other methods.
One other is what is known as, Super chunks. This is where you would cut the insulation into triangles and stack them, filling the corner completely with insulation.
You don't have to make them floor to ceiling, frankly that gets expensive pretty quickly to do every corner. If you have the budget to do it, do it, if not there's an alternative. In relation to your mixing position, you can have the center of the bass traps at ear level.
If you cant afford to treat the corners floor to ceiling right now, then later you can add on "triangle" bass traps, I'll post a pic in at the end of the post, and use those for the tri-corners at the ceiling and floor.
For the ceiling you generally have a "cloud" absorber over the mixing position and above a drum set. Don't just throw a blanket up there.
Tri-corner traps:
