Hello @deborah,
A standard poolish is equal parts water and flour – i.e. 25kg flour + 25kg water, and yeast amount varies from 0.1% to 1% ofthe flour weight. Fermentation is anywhere from 6 to 18 hours, depending on the amount of fermentation flavor and reaction you want.
Most of the time the poolish is made from 25% of the total flour in the final formula.
Hope this helps.