Just stand big sheets of ply (we use 6mm on is side for a short one, or 18mm on it's end for a tall one) up against a wall...then use hardboard to smooth the entry and exit...simples
Gaffa the boards to the floor...and wall if your able...plenty solid enough
Biggest thing I've found with wall rides is making them long/big enough for the cars to be on them for long enough to make it fun to drive, and a worthwhile feature.
I've put vids on your other track ideas thread!