Rats in a domestic property in Frome

Will people please listen to my advise - sometimes!  One customer in Frome is convinced the rats are gaining entry via the roof, when I am sure there is a drain issue.  I would either get Wessex Water out to check drains or my trusted contractor CHris from Alpharod to inspect them.  I am convinced there is a drainage fault, as it happens, nothing is being done so the rats will be back!