There are three main parts to the trike: the front power wheel (Steps 1-4), the main frame with seat (Steps 5-6), the rear steering wheels (Steps 7-11), rigging (12) and the optional cargo rack (13). The trike is built from parts from three donor bikes I got at a bike coop as I described in this "Ible": http://www.instructables.com/id/How-I-Get-Free-Bike-Parts-Legally/ A parts list is on its way (14).
Welding is required and the cost for purchased parts was roughly $100.
Front wheel 24"
Rear wheels 20"
Width of track 31"
Length overall 78"
Step 1: Front Wheel Drive
Front wheel drive has some advantages and some disadvantages. I like it because it is simpler than a rear wheel drive delta trike (no differential is required) and there is not a long chain run.
The two main disadvantages are that it loses traction going up hills because most of your weight is to the rear of the trike and that you probably will want to steer with the rear wheels.
Step 2: Harvest a Rear Fork with Pedals
Start thinking of the old right side of the rear-facing fork as the new left side of the front-facing fork.
Cut off the top tube and bottom tube right next to the bottom bracket shell.