Translation:It took me many hours to paint that room.
"it took us many hours to paint that room" = "a noi ci vollero molte ore per dipingere quella stanza"
- it took me = mi ci vollero
- it took you = ti ci vollero
- it took him/her = gli/le ci vollero
- it took us = a noi ci vollero ("c̶i̶ ̶c̶i vollero" is wrong)
- it took you all = vi ci vollero
- it took them = "a loro ci vollero" or even "gli ci vollero"
"mi ci vollero..." = "a me ci vollero..."
The preposition "a" is mandatory.
because ci isn't a pronoun here. it is a proclitic affix denoting that this verb is 'to be necessary/required' instead of the normal meaning of volere. an interesting point is that if you wanted to say that 'it took us many...' you can't use the atonic pronoun 'ci' (ci ci vollero...) you must use 'a noi'. (ci vollero a noi...)
Ci+volere is an expression. You will understand it through the following examples
It takes me an hour = Mi ci vuole un'ora
It takes me 2,3.... hours (more than 1) = Mi ci vogliono due, tre,... ore
It took me an hour = Mi ci volle un'ora
It took me 2,3... hours (more than 1) = Mi ci vollero due, tre, ... ore
Hope it helps.