My short answer would be this... A lot depends on what you mean by "rock albums" and a lot depends on whether you mean in the US or worldwide. It is hard to get concrete figures on worldwide sales. If looking only at the US, the RIAA is probably the authority. With that in mind, I would say that in my opinion the highest selling rock albums in the United States are...
1. THEIR GREATEST HITS 1971-1975 - EAGLES
2. THE WALL - PINK FLOYD
3. IV - LED ZEPPELIN
4. BACK IN BLACK - AC/DC
5. RUMOURS - FLEETWOOD MAC
6. THE BEATLES (WHITE ALBUM) - THE BEATLES
7. APPETITE FOR DESTRUCTION - GUNS N' ROSES
8. BOSTON - BOSTON
9. 1967-1970 - THE BEATLES
10. JAGGED LITTLE PILL - ALANIS MORISSETTE
I would not even be able to guess at what the worldwide top ten is. And the very first spot could easily go to Michael Jackson's Thriller if you choose to call that rock. I would say it is pop or maybe R&B if you REALLY stretch the definition of R&B.