Before building a composite deck always read the installation instructions from the manufacturer paying special attention to the required joist spacing.  Most composite decking materials require 16" on center spacing for straight decking and 12" on center joist spacing for 45 degree angle diagonal decking.  Also many composite decking materials require 12" stair stringers spacing to support composite stair treads.  If you are reinstalling composite decking over an existing frame you may need to install new intermediate joists or stair stringers to meet the installation requirements.