Building a raised area in garden

[angelboy]

I want to build a 2ft raised area in my garden, about 5m x 15m, which will have a barbeque area and an area fo seating.

Do I have to hard fill this area or can I make concrete foundations build up with concrete blocks, floor joists and topped with some kind of paving (creating a hollow void underneath)

What's the best way?

 

[Thermo]

if you are going to pave it then it will need to be backfilled.

if you want to deck it then you can leave a void.

 

[angelboy]

So I can buy hardcore/ton and fill it in?

Is that a cheaper way than using concrete blocks as the joists and filling in between with hardcore to get a level?

(S'cuse my ignorance.....not bad at internal DIY but never played with a garden before!)