I've not built one, but I'm the neighborhood keeper of an old Trac Vac that three of us use (
Trac Vac Quality Commercial and Residential Lawn / Leaf Vacuum 's ). It has a 10.5 hp B&S engine that runs a really nasty cast iron chopper/blower. The intake is a 10-inch hose. The output goes into a covered dump trailer. I fix it enough to feel like I've built it -- the quality is very good, it is just old and abused.
It has attachements that can be used with most any riding mower/tractor to suck up anything coming out of a side discharge mower deck. I mostly use my loader and rear blade to push my leaves into really big piles. Then I suck them up with this machine, which also chops them. If a branch will fit up the hose, the chopper will mince it. Rocks and things don't bother it. A big pile of leaves is well less than 1/4 its original size after I run it through this thing.
When this thing is fired up, you better make sure your dogs and cats are a long ways away. It doesn't hurt to wear suspenders and a tight belt either. It really sucks.
I've seen these things sell on ebay for a couple hundred dollars. They are well worth it if you've got as many leaves as I've got. I actually have to plow my 1/3-mile driveway because it gets covered with several inches of leaves that are slippery, and if I don't remove them, they really make a mess when I plow snow.
I've also got a leaf picker-upper with the two bins on my Cub Cadet lawn tractor. The bins can be lined with bags, or they can be dumped. As far as I'm concerned, it is not worth the effort. The bins fill up way too quick and they just don't hold enough. It jams a lot too if there is damp grass growing under the leaves.
My father-in-law has a walk-behind Billy Goat that I've used at his house. It is good for a 1/4 to 1/2 acre city lot. It does a much better job than my Cub Cadet system. But, I have to wear a respirator when I use it. It stirs up a lot of dust, plus it has to be emptied fairly regularly. When emptying it, the bag is really full of dust.
Happy Leafing,
Knute