untreated timber outside -simple question

[happyhero]

Hi I want to put up 2 3m posts outside, they will be supporting a large overhang of roof from my shed that I am building. I was going to get posts that are 5" x 5" (Seems harder to get this size from usual places I found).

Can you tell me is it ok to get ordinary untreated timber for this and treat it, or will it make a big difference to buy pre treated timber?

They will sometimes get hit by rain and as for fitting I was going to use those metpost things, I was going to use concrete type so that the posts wont actually be in contact with the ground.

 

[Jaffa72]

Depending on what finish/appearance you are wanting.There is no reason why you cant use dressed(pse) timber and treat it with a suitable preservative.Or you can use pretreated roughsawn timber if you want a 'rustic' finish.
Whichever timber you decide to use outdoors should be treated for protection against the elements.Always make sure that you apply preservative to the cut ends of the timber.Before you fit the timber it is a good idea to stand the ends in a bucket or similar container with preservative and leave for maybe a couple of days to let it draw itself into the timber.