First get a design from Wright in the peak of Oslya. (the third cave from right to left) You need to give wings and propeller to Wright to get a design Mighty Plane.

Then you can start to manufacture a Mighty Plane.

Which Roca's quest do you mean? Here is a list of Roca's quests:
1. First Test
2. Death of Roca's Father
3. Start off again with Roca
4. Undeserved Roca
5. The Fairy's Revelation
6. Strong Enemy, Frederico!
7. The Promise Under the Sky