After the painting is stretched, outer frame can be added. To frame a painting, floater frame (Option C) is the most popular way - it does not have rabbet which goes straight ahead to the bottom, like a L shape. It looks more clean. At the same time, glazing is not able to be added. 

Apart from floater frame, normal frame with rabbet could be used. Acrylic / glass glazing is optional. There are 2 framing ways:

Option A - Fix the stretched painting in the frame that 4 edges from the painting will be covered. When frame need to be changed in the future, the paint at the edges might peel off due to the touch with the wood for a long time. 

Option B - Keep distance between stretched painting and the frame edge, back paperboard become a visible border, color is based on personal preferences.