I know of a way to make them better....go to Walmart and buy some Rhino Ramps. I love a good DIY solution when it's significantly cheaper and/or somehow improves upon what's readily available, but this does neither. Rhino Ramps are inexpensive, readily available, work well, are easy to use, and have been proven to be very durable.
I don't like how they look tall and narrow, like they could tip to the side rather easy. I made some wood ramps in my teenage years, but started with long boards and nailed progressively shorter boards on top until i got the desired height. They were solid wood and I used the widest lumber I could find for stability.
While it's fun to build stuff, no way. Hollow ramps? Nails? Heavy?
And the Rhino ramps ain't hollow? They're a sold chunk of plastic? Didn't think so. And don't they fly forward as you try to drive up on them? I've used these home made ramps for 20 years made from 3 2x6's cut and stacked into 5 levels. Great when you want one side of the car higher than the other if a drain plug is at the side of the pan.