Building a staircase is an involved project. You need time and experience with construction methods to do it correctly. You need to make every measurement precise to fit the many pieces together in a safe and functional manner. If you plan to build a staircase, you can use one of several methods, depending on your ideal design and how much space you have.
A straight staircase with evenly spaced steps and no turns is the simplest stair design. Straight staircases require the most space to build. When building a straight staircase, you need to measure all of the dimensions of the stairs. This includes the height the stairs need to cover and the length. You then need to make at least three stringers, the diagonal pieces running the entire length of the staircase. The stringers need L-shaped indents for every step to be fitted into. After cutting the pieces put the stringers into position and add the risers, vertical portions, and the treads, horizontal portions, on top of the stringers.
The L-turn staircase is similar to the straight staircase with the addition of one 90-degree turn. On L turn staircases there is a landing at the point of the turn. A landing is a large flat step. Other than the landing, the basic design of the L-turn staircase is the same as the straight staircase. Build it as if you are building two staircases, one of which goes from the upper floor to the landing and the other going from the landing to the lower floor. Put the landing halfway between the floors.
A staircase with a solid cylindrical stringer with steps rotating 90 degrees consecutively is the most complicated staircase. In general it is most convenient if you can divide the number of steps by two so the stair starts and finishes in opposite directions. With this staircase, it is even more essential you measure every piece properly and accurately. This staircase takes up the least amount of room of any type.
If you cannot make a staircase individually from parts, or don't want to, you can buy one of a variety of staircases that come in precut pieces for do-it-yourself assembly. Buying a precut kit is the safest and easiest way to ensure everything will fit properly and safely. The kits come with thorough guides to ensure easy assembly.