I just finished my own shop-built air cleaner.
A friend in the heating / cooling business gave me a used furnace blower of unspecified, but generous, capacity. It's outlet is about 12" x 15". I built a box around it with a 2-by frame to keep the filters from being sucked into the blower and to give the air some mixing room inside the box. I also wanted to leave the possibilty of using the back for filtration area open in case the side openings were too restrictive. I have a three layer filter. The first filter layer is the 56 cent spun fiberglass variety to keep out large bugs / small birds. The second stage filters to 7 microns and the third stage filters to .3 microns (about .000012" -- filters bacteria and molds, some viruses). I used a total of six filters on each side (2, 20"x20" filters taped into a 20"x40" rectangle per layer) giving 20 x 40" outside filtering surface on each side (800 sq inches, not counting pleating) for a total of 1600 sq inches exposed filter surface.
That's clear as mud.
I ended up with two filters, 20"x40"x3" with a coarse outer layer and a .3 micron final layer sandwiched around a 7 micron pleated filter. Each filter is thus 800 sq inches for a total external filtering area of 1,600 sq inches. The intake is on the sides and the exhaust is out the front. There is a doubled layer of 1/2" plywood for a top to which are mounted my belt sander, grinder and task light. The whole arrangement is about 40" wide by
40" tall by 24" deep. I'll probably put some hardware cloth in front of the exhaust to keep the safety harpies at bay.
My shop is 11' by 31'. (About 1/2 my basement.)
I exhaust the air lengthwise across the middle of the floor. At the far end, it raises up and follows the outside walls to return ... carrying dust away from my face. My HF 2 hp chunk collector bleeds 30 micron dust but is between me and the air cleaner along the outside wall. It's really nice to fetch the DC bags a whack and see the dust immediately head for the air cleaner.
Cost to build? Approx. $40. I used salvaged dunnage plywood and 2x2's for the casing, glue & drywall screws to hold it together, a slap of old paint to spruce it up and salvaged wiring parts. About $38 of the cost went into the filters and I can feel the strong breeze all the way to the back wall. ;-)
Sawdust and lathe shavings still fall to the floor ... but there doesn't seem to be any dust anywhere anymore. Even when the DC is turned off, I leave the air cleaner running.
FWIW ... I still wear my respirator ... I'm down to my last pair of lungs.
Bill