In reply to Mountain Spirit:
I have no real knowledge of yoga, so i cant comment on those exercises. However, i just thought id give my opinion. Remember the term core strength relates not just to the abs, its lower back also, dont neglect it, as it will cause imbalances if your targeting the abs all the time.
Roof climbing requires good footwork and technique, such as clamping a hold with both feet.
The core exercises i do is hanging leg raises (strict form without momentum), L sit pullups, which in turn will give your lats a good workout also. ab wheel roll-out is a fun exercise, if you dont have an ab wheel, they can be done using dumbbells if you have rounded ones.
Specific lower back exercises i do is either Barbell Deadlift, good morning. Or if you have limited equipment back extensions are very good also, can be done with bodyweight, or small weight plates or dumbbells:
http://www.exrx.net/WeightExercises/ErectorSpinae/BWHyperextensionBall.html
Getting back to your original point with the yoga, the plank poses etc will work of course, but just maintaining a static pose, makes you strong in that particular position. So maybe doing core moves that require movement, IE, the back extensions and leg raises, that will sort of mimic the bending/twisting climbing involves.
And of course, to get better at roof's, climb roofs more often^^