Was thinking of rain to run off as fast as possible. If you cut them at 4 foot to go straight across, water won't run off, unless the center joist is higher (1/2, 3/8") than the outsides. Use screws, not nails.
But I was thinking more of all the 5/4 meeting on the center joist at a 45/60 degree angle. Lots of short boards, lots of screws.
That's the way I built the ramp for my father-in-law. Sorry no pictures.