Steve,
Just as a quick 'guessitmate' you can just figure the amount it would take to go around the parameter. Then figure how many places you will need extra support for bulkheads, etc and add the vertical measurement for each area and you should be very close to what you need.
Remember that when figuring cost that it will be cheaper to buy wider materials and rip them to the width that you need. Figure you total linear feet that is needed and then you can price it in the demensioned 1x or price to buy wider 1x and rip it down to the demensions you need.
Just my opinion and advise.