I would use what you have to start with - ie a dining room table. I have bought some 4 by 2 sheets of mdf to sit on top of that to make a 6 by 4 surface, which is fine for most starter games.
My longer term plan is to use lightweight internal doors (the UK type with folded card inside). These can be had in a variety of sizes, but I will probably go for 6 by 2 and a half, so that 4 doors will give me a ten foot wide surface. Most doors come 6 and half feet tall, so I will cut them down. But they can be had relatively cheaply, and are reasonable light whilst being very rigid. They will need joing when in use, so I will probably resort to the model railway technique of using hinges without the pins, that have a replaceable pin instead. Can you see how that would work? Join the two doors with hinges on the very (upright) ends, then take tegh pin out and replace it with an "l" shaped replacement. That way, when in use they are locked together, but afterwards the pin is removed and they are individuals again.