There's something wrong here. In your drawing, the top measurements add up to 17" (8.5+8.5) but the bottom measurements only add up to 16" (8.5+3.25+4.25). What are the angles of your parallelogram, and do they match the angles of your trapezoid?

I finally realized that, too!

Your top drawing seems to be

working -

How about getting it enlarged to whatever size you want it to be -

Cut out the pieces - paste them on to template plastic - add seam allowances - and just use those templates for cutting?

You will still need to match the intersections of the angles when you sew the pieces together.

I look at making your pattern a little differently. Your pattern exist of one black triangle; a gray piece consisting of 3 triangles point up, down, up; and yellow of 4 triangles, up, down, up, down. (Look at the gray and divide it into 3 triangles, 1 pointing down, middle up, next one down.) What ever size triangle you want to use will work, and angles will be correct. Just draw around your shapes without seam allowances to make the shapes you need and add 1/4" on edges for seams. If you mark your points for a few times when sewing your seams, you will get the hang of the overlaps at the ends, and the piecing will be easier. Hope I explained this so you can understand.

Excellent explanation - (I am aggravated with myself for not seeing it, too! :o )

By the way - I named this attachment "better"

I stand by my "how to pin a triangle to another piece" explanation.

Interesting how the illusion works with this - - -

After checking out the rest of those measurements I drew it up again and decided your triangle base has to finish at 4". I would cut the fabric with a base of 5" with a height of 6". After the points are trimmed it should fit perfectly, almost. the seam allowance may be a tad generous.

After my earlier disaster posting images I won't try another.

Thanks for the help! i think the 6 1/8" top triangle will work. I was done fustzing with it last night and I'll take another crack at it tonight.

I'd paper piece the bock as well to ensure a lovely point.

On bearisgray's drawings, you can see that the triangle piece does not need the tip. If you laid your template/pattern on a strip, it would not need to be wider than the other strips, and you cut the triangles with no tips. That gets cut off anyhow.
Sewing with those tips gone makes it much easier to line up the pieces. I did triangles with strips around, and found it was much easier after all the tips were gone.