There are two common pronunciations for oo: typically "book" and "boot".
With "r" it is pronounced as in door or floor. That is regular, and you'll see the same reading in moor, poor, boor (but not hooray, which is formed as hoo-ray)
The other readings have various reasons: Brooch (a type of jewellry) was deliberately spelled with "oo" to distinguish it from "broach" (a large pin)
There are words with the prefix "co" in front of a word starting with o. This explains "cooperate" and coordinate (and there are no similar common examples)
Flood and blood seem to have changed pronunciation. 600 Years ago they would have had the same vowel as in book and boot. The modern pronunciation started as a dialect variant, which spread. The same dialect variant didn't catch on for other "oo" words. flood and blood are the only words with the -lood pattern.
Zoology is pronunced with the regular "oo" sound, but it followed by an "o" sound of "ology" It is really zoo-ology but a triple letter has been suppressed.
There's no rule