The final design of your frame starts with the surface on which you paint.
If you use traditional canvas/linen stretched on canvas stretcher bars one important item to remember is to select stretcher bars which can be keyed out. Some people think they can cut four lengths of wood, join them together with nails or screws then stretch canvas over the frame they made. Yes, it can be done. But what results from that ends up needing to be un-done. Canvas/linen is flexible, and, over time, depending on the atmospheric conditions, will sag. If your canvas stretcher bars are joined at the corners the painting will always sag and buckle. The surface of a stretched canvas needs to be drum tight and canvas stretcher bars with keys or the Lebron type stretcher bars are the only way to go.
Lebron-type canvas stretcher bars
pre-cut canvas stretcher bars
Other surfaces artists like to use are cradled panels, masonite or birch panels, and masonite panels which have linen or muslin mounted to them using rabbit skin glue. If you choose the latter options, an additional cradle will have to be built to use a canvas floater frame.