If you have never built a kit, the jump from ARF to scratch built will be one giant step. I would suggest you build at least one kit before trying a scratch build. That way you can begin to see all the many little details that have to be worked out and the way things go together. After several kits you will have developed the skills as well as the understanding to complete a scratch built project. If you have a good detailed set of plans the scratch build will be a little easier, however if you intend to design and build from scratch without some kit experience it will be a very difficult undertaking.