Wood is the cheapest frame solution overall with different choices in wood quality. We use C24 structural timber which is pressure treated to prolong the life with the choice to have it taped also to give an extra water barrier once the boards are laid. 

We can Also treat the frame a black stain to add protection against water but also to see no frame through the gaps on the board.  All our wooden frames are off the ground avoiding the chance to soak up water and allowing air flow to assist drying.  Wooden posts are used but we do our utmost to protect from water, sometimes its worth paying for composite posts. Heavy duty membranes are also installed to avoid plant growth. 

Using a joist tape to the tops of the joists add extra protection against water ingress and possible rotting. It allows water to drain away instead of sitting on top of the joist.  We use this on composite decks as a cheaper alternative to composite framing.  Just provides that extra peace of mind from rotting. 

We can also treat the frame to a black stain instead of tape which adds another layer of protection against water on top of the already treated timber. 

We use Ecowood technology where the timber is made from 100% recycled plastic. This does not decompose or attract mould or rot giving you peace of mind and longevity.  Our supplier of composite decking provides a 25 year warranty on the boards so composite framing will stand the test of time. It goes without saying really that this is dearer versus wood however in the long run potentially works out cheaper. 

Guaranteed not to rot however due to the plastic content it can move in high temperatures, we only advise to use this is really wet area's.