Taxan

I have been asked to build a riser approximately 15 inches high strong enough to support a two seater leather sofa. This riser is to be positioned on the floor in a home cinema room to create a tiered seating effect. The floor of the cinema has under floor heating installed. Do I need to know anything regarding converting the floor or any weight restrictions etc before installing the riser. The riser will be made from 8x2 plus 6x2 timber. Any advice or help would be much appreciated.