Stairs that do not have any steps are essentially worthless; they are simply a series of zigzag upright planks that go from one level to the next. This is analogous to a vehicle that does not have seats or a home that does not have doors. Treads are the very minimum need for a functional staircase, although risers contribute to the appearance of completion in more conventional stair designs. Take your time and carefully cut each tread and riser out of plywood, hardwood, or any other material of your choosing. When the treads won’t be covered by carpet, you may even be able to get parts that are manufactured to order with rounded lips. Stay away from particle board and other comparable manufactured wood items because they expand and buckle when they come into contact with moisture.