Re: it seems i cannot choose my attributes

In the DA:I universe, it does! Sadly, as you noticed the game does not allow you to freely choose your attributes while leveling (see also here). Rogues will always gain Dex/Cun, Mages get Will/Mag and Warriors get Str/Con after a level up.

Comfort yourself knowing that a rogue works best with high burst damage output (dex/cun). It may 'seem' that you are squishy, but trust me on saying that a bit later in the game (not so far) you notice they're not that squishy as you think they might be!!

//edit

desertrat576 is right, you only increase those skills passively by choosing the appropriate skills. My apologies.