Hello I wonder if there is a way to have a separate template per page or category

Thanks

this can be done easily, create different page types,

lets say my page type is DefaultPage so I am going to save my page in the /mysite/code folder

now to have a separate leyout from the others I am creating a new template for the DefaultPage and save it as DefaultPage.ss in the /mysite/templates folder.

Then when the site is being retrieved the DefaultPages are viewed with that Default.ss file you created not with the /themes/<your theme>/templates/Page.ss

Thanks, where do you set the page type.

Generally in the mysite/code/ directory.

I'd suggest reading the tutorial which gives an introduction to this:

http://doc.silverstripe.com/doku.php?id=tutorial:2-extending-a-basic-site

An upcoming feature in 2.4 will be the ability to select a custom template without a page type which will be quite handy for those pages which don't 'need' any custom code just a separate template. There is a ticket on open.silverstripe.com for this.