Here's a sour dough ciabetta formula that has worked for me using baker's percentage. Be careful about the hydration % since the absorbtion varies from flour batch to batch.
Whole Wheat Flour 39.6%
White Wheat Flour 60.4%
Water - 89% - use double hydration method, initial mix use 70% hydration, after dough develops add remaining water at 1st Speed.
Sour Dough - 31% - my culture is 65% hydrated
Salt - 1.98%
Dough is very slack and hard to work with if you don't have experience, cut down the water percentage to what works for you.
Fold a couple of times during fermentation for added development. Good Luck.