parents phillip and gaby beckle-raymond discovered a leak in roof .
hired builder to fix problem at their three bed london home .
he took roof off and then disappeared with £ 10k of their money .
sub contractor botched efforts to give them loft conversion .
he charged £ 7,000 for parts and labour but left them with unsafe building .
family had to live in one room for six months as home had no roof .
rain water got in causing ceilings to collapse .
britain 's horror homes is on channel 5 tuesdays at 8 pm .