To build ReactOS, you will need a suitable Build Environment.
As the current ReactOS Source Code is only compatible with specific versions of the compiler tools, only the official ReactOS Build Environment (RosBE) is supported by us.
So if you want to report problems, please first make sure that you use the latest version of the ReactOS Build Environment.
Download the Build Environment
There are two ReactOS Build Environments available, a version for Windows NT-compatible Operating Systems (Windows 2000, XP, Server 2003, ...) and a version for Unix-compatible operating systems (Linux, FreeBSD, ...).
Additionally, a Subversion client is needed to obtain the current source from the ReactOS Subversion repository. Read that page for more information.
After setting up your build environment, see Building ReactOS for futher information.
You may want to use an IDE, so refer to this page.
Questions or Problems?
If you have problems or questions concerning the Build Environment, it's the best to ask in the #reactos-rosbe IRC channel.