I'v used svn://svn.berlios.de/codeblocks/trunk/src/sdk to get sdk.
That's the right one.
Please do note that you will need compatible import libraries for
codeblocks.dll and
wxmsw26_custom.dll too, if you want to build a plugin.
I am not aware of any import libraries compatible with the nightly builds being available for download (but I may be wrong). If you ask Killerbot, he might put them up though.
Alternatively, you may want to check out the complete source tree, not just the
sdk folder (go one directory up) and build Code::Blocks from source. It only takes like 5 minutes alltogether (if you have a working wxWidgets), so that should not be an issue.
It is also possible to make import libs from the dlls coming with the nightly builds, but that is a pain. Lastly, it is possible to use auto-import, too, but that is almost as much pain (and sometimes, it fails too).