I install these islands all the time.They are steel or stainless steel and come in different configurations such as dog bone,oval and square end.A standard setup is 4' wide by as long as you want to go and they come in 9" or 13" depths.They are set,braced and then poured with concrete.I guess you could use them as temp forms,then remove but you would have to remove all angle and bracing from inside then make sure you braced the outside well.1 yard concrete= aprox 3000 lb. Bill