everything is free available. but to set up your build env needs time. and if you are not a programmer i'd say you are lost, as it needs some understanding of what you do.
in general the following steps do it:
setup the build env and take a very small project and build this. if it works then you are sure the build env works
grab the source from a cvs/svn/git whatever reporitory. of course this needs again cvs/svn/git or whatever knowledge
try to build it. usually either a cmd file or a configure script does the trick
now look at the errors you get and probably you need to download some dependencies.
if there are build them and if all is built try the project again.
i wish you good luck in building ooo.org

and i can tell you it's not a one day job. if you want a working exe buy it or take at least a week of when trying to build. as you need at least that amount of time to do the setup and all stuff right.
regards
Silvan
QT4 project lead