Building a plane from scratch is a lot different from designing a plane from scratch. To most of us "Scratch Build" just means it was a set of plans and not a pre-gathered box of the needed parts in a kit. Get a set of plans for a Telemaster or Sig Kadet and you're gold.

Are there design limits? Size, weight, engine, length of runway? 95% of .40 engine size planes with enough power and wing area will lift an egg.

Do you also have to build the engine, actuators and transmitter/receiver? Now there's a challenge.