Design Form/Fields in Sandbox and Export to Production

Description - We would like to design fields and forms in the sandbox to test items there prior to implementing in production. 

Why is this feature important to you / how would you like it to work - While we can create items in production and then have the sandbox refreshed, we cannot design something in the sandbox and move to production.  Often part of the testing requires changes to other areas that we don't want to change in production until we know it works. We want to create mockups and test in our sandbox that we can then push to production without needing to recreate all the work we completed in the sandbox. This would be a great timesaver.