Decks provide a great cost effective method to provide a seating area, they can be dug down to be flush with the ground level or built up and raised above, with steps and ballustrade if needed.

I use pre-treated tanalised deck boards and sub-frame timber and I ensure the sub-frame rails are spaced no more than 50cm apart to ensure that the deck does not flex and move when walked on. I always use treated deck screws (not nails) to secure all the timber and the deck has a weed suppressant membrane underneath. 

Pre-treated timber sleepers or deck boards can provide great raised planting areas. Please see the gallery below for examples of decks and raised planters I have built in the past.