PackageTemplate
You can find a template for a standard cabalized package got from Hackage here. Most of Haskell packages can be obtained simply by copying this directory in debian/ in your source package and then filling in the gaps (of course, this doesn't take away from you the responsability of testing, checking with lintian, building under a chroot, ... your package). You can obtain this template directory using darcs:
darcs get darcs.debian.org:/darcs/pkg-haskell/tools
debian/control
'Build-Depends' need not include the packages provided by ghc6. The list of such packages can be obtained with
apt-cache show ghc6 | grep '^Provides:'
or
apt-cache show ghc6 | sed -n '/^Provides:/ {s/^Provides: //; s/, /\n/g; p}' | sed -r 's/-[-.0-9a-f]*$//' | sort -u
Each (build-)dependency should be on a line of its own -- this makes diffs easier to read.
Remember to check the build dependencies using pbuilder (or cowbuilder, or debomatic, or somthing equivalent).