Each card used in the recipe of your custom coaster adds its own stats to the total. Adding special inserts, or a train or a station modifier increases the stats of the base set. There is also a value added for the design of the track layout.
The perfect design for each coaster varies - it's a challenge to find the perfect recipe. Wooden and Hyper coasters should have a lot of bunny hops and air time. Steel and Inverted coasters should include a lot special insert and inversion. Accelerator should well...be really fast, and not last too long or else they get too intense. Winged and Inverted coasters should be a good balance of many factors: drops, inversion, speed, height and banking.