Build a parlay and see the combined probability and expected value of the legs together, including how correlation between them changes the real payout math.
Most parlay tools multiply prices and stop. Correlated legs do not behave that way, and the difference is usually where the value goes.
Multiplying individual prices assumes the legs are independent. Legs from the same game usually are not — a quarterback throwing for a lot of yards makes his receiver's yardage more likely too — so the true combined probability differs from the naive product, and the payout should reflect that.
A parlay whose legs all come from one game. It is the most correlated kind, which is why books price them separately rather than simply multiplying the legs.