There is no right or wrong answer to this question. If you create something that gives you an intellectual property interest in the creation (such as a copyright), you will retain that interest unless the manufacturer you refer to requires you to sign a “work-for-hire” agreement. A “work-for-hire” agreement will serve to transfer all of your rights in the creation to the manufacturer for what ever compensation you may agree upon. If you do not sign a “work-for-hire” agreement, then your approval of the manufacturer’s use of the creation constitutes a “license.” You may agree upon a fixed fee for giving the manufacture the right to use your creation or you may ask for a continuing payment based upon the profits earned by the manufacturer from the sale of your creation (a royalty). Before going forward, it would be in your best interests to have the arrangement reduced to writing and reviewed by an attorney who is knowledgeable in the area of intellectual property.