You can build it at http://win-builder.r-project.org/upload.aspx, just don't forget to change the DESCRIPTION
file to include your email address as maintainer.
It is actually quite tricky to build it because Rtools has some fixed (?) paths and it is looking for libraries at specific places, so you need to put them there. We build it with something like
...
if ! (subst | grep -qi ^d:); then
subst d: c:\\
fi
pkg=`ls igraph*.tar.gz`
zip=`echo $pkg | sed 's/.tar.gz/.zip/'`
rfile="r-win/${zip}"
OLDPATH=$PATH
PATH=/cygdrive/c/Program\ Files/R/R-default/bin:/cygdrive/c/Rtools/bin:/cygdrive/c/Rtools/gcc-4.6.3/bin:$PATH
LIB_XML=c:/RCompile/CRANpkg/extralibs64/local R CMD INSTALL -l . $pkg
zip -r ${zip} igraph
PATH=$OLDPATH
...
This uses a cygwin shell. You can get the extra libraries here: http://www.stats.ox.ac.uk/pub/Rtools/libs.html