Prerequisites of Building Chrome OS

System Prerequisites

1. Linux distribution : Ubuntu 8.04 (Hardy Heron).
2. Disk Space : 10 GB at least.
3. 64-bit system. (better)

Software Requirement

1. Python >= 2.4
2. Perl >= 5.x
3. gcc/g++ >= 4.2
4. g++-multilib >=4.2
5. bison >= 2.3
6. flex >= 2.5.34
7. gperf >= 3.0.4
8. pkg-config >= 0.20
9. libnss3-dev >= 3.12
10. libasound2-dev
11. libgconf2-dev
12. libglib2.0-dev
13. libgtk2.0-dev
14. libnspr4-0d >= 4.7.1+1.9-0ubuntu0.8.04.5 (ubuntu0.8.04.1 causes duplicate dtoa references)
15. libnspr4-dev >= 4.7.1+1.9-0ubuntu0.8.04.5
16. msttcorefonts (Microsoft fonts)
17. freetype-dev
18. libcairo2-dev
19. libdbus-1-dev
20. wdiff (optional)
21. lighttpd (optional)
22. php5-cgi (optional)
23. sun-java6-fonts (needed for Lucida) (optional)

Check this site for more details.