When was rohm gmbh sonthiem brenz sn 118175 made and the worth of it?

Rohm, or RG, was a maker of low dollar handguns of indifferent quality. From the mid 50's to about 1968, their products were imported from West Germany to the US. Import was blocked at that time by the 1968 Gun Control Act for most of their products- they could not meet the tests for size, metal composition, etc. Company no longer is business, no public SN database, so that is as close as I can get. Value anywhere from $10-$50 for MOST of their revolvers, depending on condition. You did not give us a model or caliber.