I could tell you, I believe.
  A longbow to a modern American bowyer is a just a bow that has straight tips.  To almost everyone else, this is a flatbow.  Nowadays, we call the traditional longbow an English longbow, or ELB.  This is high stacked, as opposed to low stacked, as you know; this refers to depth.  A high stacked bow has lots of depth, not so much width normally, a low stacked bow is flat or nearly so.
  Yew is technically the only wood to use, the traditional wood.  You could use elm, ash, osage, whatever, but you won't get as good results, and they will follow the string - this is unavoidable.  I couldn't give you dimensions because I don't know what poundage you want, I don't know what wood you will use, or whether you want a raised handle or a proper longbow which bends through the whole length.  Johnny has made some great examples of longbows - pay attention to any answer who might give to your question.

Are you talking about a elb(english longbow) or can it be any bow thats long? For a eastern woodland long bow you could make it  71 inches long, 1 1/2 inches wide,  5/8 inch thick at the handle, 11/16 inch at tip of nock, thickness at nock 7/16,
and come out with a 65 lb bow. I'v made one like this sept for
I made it 68 inches long and 50 lbs so it was a little thiner.
You can make this bow out of just about any kind of hardwood. I made mine out of a Red Oak board from Lowe's.

Out of curiosity how are we suppost to know what grows around you it we don't know were you live?

I love those eastern woodlands bows, henryblowery.  Beautiful.  And they are not as picky in terms of what wood works.

How about an elb..- actually a welsh longbow.. which was brought over from the scandinavians anyway..
Name any type of wood that grows in america. I probably have access to it.

I have a supplier who deals in exotic woods. his name is Slim Maroushek. Im pretty sure he had a website, and me and him are pretty good friends, so I think I might be able to buy either a stave or a plank...

no.. probably should go out and buy it. Maybe amazon stocks it.

If you get  TBB #1, I suggest you read the Design and Performance chapter many times. It is some of the best
information ever written by man on the subject of constructing bows. I think I would've bought the book simply for that  chapter alone, but there are many other things in the book that are absolute gems of knowledge. If you are serious about making a good shooter, that is the place you should start.