Because you apparently do not know how a bow specifically functions and what specs are best suited in accordance with your purpose, you physical specs, and your shooting form. Hopefully, some other experienced shooters that have built their own bow, or tried and was not successful, will jump in here.

I also, would not begin with a "longbow" before you learn the basics of proper shooting form, which, imo, would best be done with a recurve if you plan to shoot only a "stick."