I used 3/8 in sheet iron with holes in it and some supports. Then painted it and striped it yellow/black with safety/non slip tape. Gets past the city, allows water to flow under it, and 'just' works. I have a high crowned rode and steep driveway. I wish I had one as gentle as in the pic above. My ramp is nearly 3.5ft wide. But., build it right it still looks good and can pass local safety stuff if that exists where you live....oh wait, you live in the same place lol. When I get my car fixed I can show you what I built.
oh, and I just saw your username, and yes (separate subject), I should be tackling the engine next weekend if about. I will have clam off and basically we will step through the entire supercharger install process (backwards, then forwards!).
[for other readers] Sorry for the rambling!