You can surely say both.
2-o-o-1 should be more standard, but if, for example, it is room 01 on the 20th floor of a hotel, 20-o-1 would carry that additional information as well.
And of course, there's still the standard "two thousand (and) one".
December 1, 2015
1
1
Still haven’t found your answers?
Write down your questions and let the native speakers help you!