Here you go this online calculator will assist you in determining the force required to bend sheet metal
Press Brake Bending Force Calculator - Pacific Press Technologies, Inc.Pacific Press Technologies, Inc.
inter in you parameters and the calculation will be interactive with each change in material thickness, length die depth / width punch radius material tensile strength , ETC.
You didn't mention the thickness of your intended project but if it is anything more than light Gage stuff, remember if you are considering building a press brake or conjoining 2 ready made machines of the size you are looking for you will need to have a floating foundation poured to accommodate the machine no normal shop slabs can withstand the punishment a machine of this size can create on its foundation.