For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mnhauke:sweethome3d/openSUSE_Tumbleweed/home:mnhauke:sweethome3d.repo
zypper refresh
zypper install SweetHome3D
For openSUSE Leap 15.1 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mnhauke:sweethome3d/openSUSE_Leap_15.1/home:mnhauke:sweethome3d.repo
zypper refresh
zypper install SweetHome3D
For openSUSE Leap 15.0 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mnhauke:sweethome3d/openSUSE_Leap_15.0/home:mnhauke:sweethome3d.repo
zypper refresh
zypper install SweetHome3D