Do you have the specs on the small side platforms ....
I made mine by ripping 2x4's in half lengthwise and using those to make a frame the size I wanted (roughly what Chuck did, only mine are roughly 7' long). Then I sheathed the frame with flake board because it was so much cheaper than plywood. I put cross braces across the top and bottom (they resembled ladders before I sheathed them, and a couple of cross braces on the sides). I assembled them using long drywall screws - everything was sourced from Hopot.
Note if you make them only 4' long, you will find that your feet hit air half way up the ramp, or you will need someone to move them forward to complete the transition from grade to lift. Yes, I've driven my bike up the ramp, but I still do it too slowly for balance w/o outriggers. Since the HF lift is on wheels, I block it so it cannot roll when I tap the brakes once the bike is on the lift. I usually drive the bike onto the lift, work on it, then turn it 180º and install the lift on the front so I can ride it off. If you do this block under the front overhang so the lift does not tip that end down as you ride off (don't ask how I know).