Climb down the roof and Climb down from the roof have two different meanings in English. The former implies that you are moving from a higher point on the roof to a lower point (but staying on the roof), the latter implies that you are on the roof and are climbing down to the ground. I had assumed that this sentence meant the latter. Could it mean both?
ska here expresses the determination of the speaker: s/he has decided to climb down from the roof. I feel that if you say should in English in this sentence, that would rather mean something like 'ought to' – the speaker thinks it would be a good idea, but they haven't decided to do it. So I don't think it's a very good match.