RAISED DECKING and....

Hi All,
I am looking to make up a raised decking area of 13ft x 13ft some 5ft off the ground at the highest point on a sloping site.
It will be 'free standing' on 4 Oak posts either 6" x 6" or 8" x 8" sitting on concrete pads.
4" x 2" will make up the 'framework' set in and bolted to the posts.

Additionally on top of the deck I want to create a structure with roof which will also be in Oak with small clay tiles on top.
I have a concern as to weight etc being carried by the 4 posts as well as the span and wonder whether anyone can offer suggestions as to sizes of timbers considered or points to watch out for etc.

Thanks in advance for any thoughts.

Don't use 4x2. Use 6x2.
Don't use 4 posts. Use more.
Don't sit them down onto pads. Anchor them into the ground.
Do fit a hand rail

Lots more posts on here on how to build a deck. Off out now so dont have time to give a bigger reply, sorry. Read, read and read. (oh, and search)

AS this will be "Free Standing" you will need more posts, although using 8x8 Oak posts will be fairly sturdy under normal circumstances, on a free standing deck they wont be safe enough especially as you are having a structure on the top of the deck as you will have to account for the weight of that plus people who maybe standing on the deck and furniture. its all very well thinking well it will be just me and the wife but if you have friends and family round then the number of people will naturally greatly increase the load on the deck!

This is quite a hard one to work out without seeing the area, as you would have to know what the soil is like for foundation pads to be constructed etc and so I would recommend that you bring in a specialist to check the ground and advise you before attempting any construction yourself.

If this is not designed and built correctly chances are the deck will become unstable and collapse which is of course very dangerous especially if people are standing on it at the time!

Also as part of the deck will be raised by 5 foot then nothing but 6x2 joists minimum should be used!

Check out the following site as well http://www.decks.com/

Thanks everyone for the help so far.

In view of the comments I have modified my thoughts and will increase the number of support posts to 3 6" x 6" Oak posts on each side from the 2 per side planned - making 6' centres on the outside of the structure.

I have also modified the timber side 'rails' and cross supporting members to 8" x 2" with additional supporting posts in the centre of the structure.

The posts will sit on poured concrete on solid ground and be 'bricked up' approx 12" to keep the wet from the base as well as provide some additional support to the structure.

Any more thoughts on the changes proposed would be appreciated.