How can I calculate the necessary amount of 
wood I  will need to build a Lightning?

Hi Paul,

>Any advice for quantity of lumber necessary for building the hull?

Calculate the area of the hull from the plans (just rough calculations such
as length times tallest height of side times 2, plus similar measurement of
bottom and decks), then add about 20% to allow for waste.

>Board length

As long as possible (a little longer than hull length if you can find such
stock) - this makes life easier, however short pieces can be used, it just
means more time and work to scarf them together to get the length you need. Generally, most builders purchase boat lumber by the board foot in large quantity. When purchased in random lengths, the price is usually less than when you specify length of each board.

> I am living far from any decent wood supplier

Check out the classifieds in WoodenBoat Magazine and Messing About In Boats. If you still can't find anyone near you, try a computer search for
saw mills. You are bound to find someone within reasonable driving distance.

> and would like to keep cost low.

Sorry, but I can't help you with this one. I have a sign hanging on my
office wall that says: "Definition....boat (bot), n.- a hole in the surface
of the water, into which money is thrown". 

Regards,

Paul J. Bennett
Marine Engineer, Naval Architect