We explore the formation of Schottky barriers by adsorption of Ge overlayers onto single crystal Ni and Ag substrates. The results are compared to earlier results from Si-on-metal systems as well as interfaces formed by the metal-on-semiconductor deposition sequence. We find that Ge overlayers on Ag form extended interfaces with the creation of an intermediate metallic phase - whereas Ag on Ge forms abrupt interfaces. However, the Ge on Ni interface is found to be abrupt. For the resultant p-type Schottky barrier heights we report values of 0.18 eV for Ge/Ag(111) and Ge/Ag(100) - in agreement with the Ag-on-Ge value - and of 0.17 eV for Ge/Ni(111). The pinning strength parameter derived from our data is S = 0.11 eV, in agreement with the value for metal-on-Ge interfaces.