Domestic/Signal Box Windows. Although Ratio does not have a Builder's range in OO gauge, we have grouped these kits here in a similar way to the N gauge Builder series to help scratchbuilders. These are all parts from kits that we have made available seperately to help you add detail to your models. Of course you can use the parts also to extend your kits projects. For example, kits such as the Coal Staithes or Oil Tanks could be combined to make a large fuel storage fuel.