• clone git://gitorious.org/qt/qt3d.git
• switch to branch qt4 (git checkout qt4)
• run dpkg-buildpackage -I.git (with or without -rfakeroot)

First issue: the dependency to "libqt4-declarative-dev (>= 4.7.3)". Not even sure this package exists on Ubuntu. In my system it wasn't there. Changing it to "libqt4-declarative (>= 4.7.3)" goes on.

Second issue: after whole build of Qt3D, the debian package creation fails with this error:
dh_install: libqt4-3d missing files (usr/lib/libQt3D.so.*), aborting