Really, the easiest way to cut those center pieces is to just wing it :) Lay out the frame, and then lay the longest single cross piece over until centered on corners and mark. Cut ends to points as shown above with a circular saw following your marks. Then cut your two remaining cross brace pieces in the same manner.

Now lay out the fence slats and measure and cut your 1x4s to fit. Nail on with 1 1/4" nails and glue.

Add remaining sides with 1 1/4" finish nails and glue.

TIP: Pocket hole jig users may wish to build frame first with 3/4" PHs and 1 1/4" PH screws.

Attach cross bracing with 1 1/4" finish nails and glue.

Barn door done deal!

Now this trim will finish off the non sliding end of the frame. You could also add to bottom and top, and you could attach additional trim to the sliding end of the door to completely trim out.

To save money, Kristen layered drawer slides as shown above.   Genius, I say! For more details and tips, you must read Kristen's blog post here.

Then attach slides to barn door and hang ... you'll probably need to do some adjusting to get things just right. Kristen gives lots of information in her post on how she hung hers (and lots more details), and I highly recommend you taking a second to read. Thank you Kristen!