I have recycled A LOT of seed this past year. I am buying 1/2 to 1/3 less seed now that I have this saver.
I took a photo from a friend's set-up and went to Lowe's hardware store to get the parts. This was after a trip to Home Depot resulted in them not having all the parts.

Here are the parts described:

Home depot sells buckets for 5 dollars and a simple vacuum that snaps right on top of a standard 5 gallon bucket for $19.99 This is what I use for general garage clean up and the seed saver. The red knob (part D) is to adjust air input so you're not getting too much suction and good seeds in the vacuum. You connect the vacuum hose to part F.
If I have about 5 pounds of seed to be processed, I use a large scoop and pour it in the funnel and a brisk pace. In less than 5 minutes I'll have about 4.5 pound of good seed to be reused.
As for the dimensions, I used the "that looks about right" method. The door is a 7 foot door for comparison.
Good luck!
-Steve