If there is one thing i hate its cockroaches so I can fully understand what you are saying... you will never find a house that has NO cockroaches at all... what you need to do is to get your house professionally sprayed where they give you a 3 month guarantee and then you need to ensure that this is kept up every 3 months. It is the only way you can ensure your house will be cockroach (and other insects free).

I dont know how much it costs there to have it done but here it cost BD 20 (around QR 199) but its well worth it believe me....