How do i go about building a false/fake fireplace, as to install an insert style combustion heater?

I want to install an insert style combustion heater, but need to construct a fake fireplace. Where do I go to find the best way to either build or buy what I am after.How do i go about building a false/fake fireplace, as to install an insert style combustion heater?
The dealer that sells you the insert should have displays and catalouges of pre-fabricated fireplaces.