I have an open fireplace, I am having a Regency woodburning insert installed anyday, I have been swamped and have yet to build my hearth extension, I need this done so he can go ahead with the installation. What can I build that would be safe easy to do and not too expensive and I dont want to fuss with tiles, doesnt need to be pretty, just safe, the extension is flush with the existing fireplace and i have hardwood floor, I am gonna go 20 " out, this should be plenty, there is no current hearth at all, could i just use cement board and some kind of fireproof sheet metal? until i have the time to build something pertty?