Normally,

remctl xvm-dev build precise-dev invirt-base $branch

If you need to set up schroot/sbuild and build manually,

sbuild-createchroot --arch amd64 --components=main,universe,multiverse --verbose bionic /srv/chroot/bionic-amd64-sbuild http://mirrors.mit.edu/ubuntu
echo "/tmp            /tmp            none    rw,bind         0       0" >> /etc/schroot/sbuild/fstab
schroot -c source:bionic-amd64-sbuild -- apt install debhelper python3-all-dev python3-setuptools python3-debian python3-apt python-minimal

Then to build a single package,

git clone --recursive git://xvm.mit.edu/invirt/packages.git
cd $(mktemp -d)
git --git-dir=/root/packages/invirt-base/.git archive --prefix=invirt-base/ $branch | tar -x
(cd invirt-base && schroot -c bionic-amd64-sbuild -- dpkg-buildpackage -us -uc -S)
sbuild -v -d bionic --arch amd64 invirt-base_*.dsc