I have built a number of ramps and have used almost every surface option.
Including gator skin. I live in whistler, Canada, pretty harsh wet weather conditions, with snow for 3-4 months a year.
Worst is standard plywood. It will begin to chip up and become unskateable
Masonite is one step up from plywood, out doors it will begin to fall apart.
Indoors it lasts longer but is very dusty.
Birch plywood is your good option. If it's outside you can paint it with a good marine paint.
This will seal it and it will take longer to start chipping and have better weather resistance.
Gator skin. I think this is a good product, not as good as skatelight but it is significantly Cheaper. I built a ramp with this two years ago. It made it through first winter no problem. I haven't checked how it survived this winter but I'm assuming it's going to be fine. I built another ramp 6 years ago that we surfaced with another similar product from this company. This was before they made gator skin, it was a counter top material made from wood pulp, plastic and resin. Same as gator skin. That ramp made it through five winters before any issues. Last summer we pulled up the surfacing and patched The plywood sheeting underneath that had rotted out. I skate this ramp at least twice a week in the summer and it's still good to go.
Skatelight is obviously the best for outdoor wood ramps. I built a wood public outdoor park out of treated lumber and Skatelight.
This park lasted for over ten years. And after the wood finally rotted out, I salvaged some of the skatelight for an indoor ramp in a
Skateshop, that gets heavily skated. Skatelight is close to indestructible.
Concrete is by far the best material for skateboarding but it is also the most expensive and hardest to build with properly.