How to Build Your Own Decking Area | Essential Home and Garden Apr 14, 2017 . To build a raised deck, you must prepare the site use pegs and string to mark out the area, and ensure it is clear of any plants and rocks. You will need to ensure that the sides of the deck are completely square you can do this using the 3-4-5 triangle method. For a raised deck, you will need to use joist..