Decks are often built before patios in order to allow frost footings to be placed without disrupting the concrete slab. It is best not to attempt building both projects at the same time so you can focus your attention on the job at-hand. If you are planning on installing a concrete patio below the position of your stair landing, you will need to adjust your stair design to properly land on it once it is completed. You may need to postpone your final deck inspection until the patio is installed for the stairs to meet the uniform riser and tread requirements. In the meantime, you should brace the bottoms of the stairs.
Some deck builders install a concrete landing below deck stairs at grade. The minimum size for a stair landing is 36" x 36" in front of the stairs. You will want to rest your stair stringer on 12" of the concrete landing. In this case, we are pouring a 4'x4' pad.
Find the location to build your concrete forms. Use a level and a tape measure to determine your elevation. Use the Decks.com Stairs Calculator to determine your stair run.
In this case, we used the joist material from tearing down the deck for the concrete forms. We used wood stakes to secure the form.