Find a free floor plan building tool online. The FloorPlanner website has one.
Select what you want to start with. The FloorPlanner tool gives you the option of starting with a completely blank sheet, a room, or a full sample floor plan. Click on your preferred option to get started. If you select the room or sample floor plan, you will choose the floor plan or room shape you want to start with as well. If you choose the room selection, you will also have to choose the dimensions of the room.
Draw a room, surface, a single wall, single line, or single dimension, or add a door or window and comments using the tools under the heading "Construction" on the right-hand, top side of the screen. Add stairs, or other extras that you want by using the tools under the heading "Library" directly below the "Construction" tools. Play with the floor plan until you have completed it to your satisfaction. Once you're done, you can view a 2D and 3D version of your floor plan by using the 2D or 3D tabs on the top, right side of the screen.
Click the picture of the printer found on the farthest right-hand corner of the screen. If you want to save the plans, you will have to get an account with FloorPlanner to do so. However, FloorPlanner does have a free, basic account, which allows you to save your design.