Guitar tops and backs are radiused to increase section strength and reduce moisture content-variation shrinkage stresses. If the wood dries lateral shrinkage will cause a change in the arch radius before cracks occur.
There are many books that tell you how to radius the top and back. This free build manual will help you understand building.
https://www.stewmac.com/freeinfo/i-W...V.doc.1219.pdf
Don't start until you understand what is required. Most critical is neck angle which starts with the neck block shape.