Joe, I’m guessing you don’t want the table top look of just plywood sheets. Nor at the price of plywood do you want to cut out curved sections and then figure out what to do with what’s not used. If you enjoy woodworking. I’ve seen a few layouts incorporate what’s called spline roadbed. Basically it’s 1/4 “x 1” strips cut from wood stock with a table saw. Sort of like lattice. They flex to sort of a perfect circle with built in easements. Used a lot by those that handlay track. You build the width up by putting little spacer blocks between each strip. You stagger the joints. O gauge probably requires 5 strips. You then either purchase or cut your own homesote roadbed and glue it to your wood risers. The homesote has slots cut into and will bend to follow the spline. It does save you some money and your layout will have a non sectional track like look to it. The curves usually end up where you want them to be but the have a nice flow like they weren’t drawn with a compass.
Pretty sure this is covered in Linn Westcotts book and there are numerous videos on line how to do it. Works well if you want your layout to have hills and valleys.
