Choosing Your Canvas
You can purchase precut floorcloths but the canvas used for these is very coarse, which may suit your painting style, but if any moisture permeates the perimeter the canvas will become wavy and this cannot be corrected. I prefer a fine weave that allows me to create everything from crisp stenciled motifs to finely detailed paintings. Roclon all purpose cloth is a popular surface for creating banners and floorcloths. It has a fine texture weave that doesn't interfere with detailed painting the way a coarse canvas might. In addition, Roclon does not need to be hemmed, stitched or glued! It can be cut with scissors or a rotary cutter and ruler.
Preparing Your Canvas

Decorating Your Canvas
Base coat the canvas in the color(s) of your choice then stencil or paint as desired. If painting is not your forte then, in lieu of priming and base coating, consider mounting fabric on the canvas. This can be applied as a single piece or in a patchwork manner. Mount the fabric using the wet mount method shown here.
Finishing Your Canvas
For the best protection always finish a floorcloth with an indoor/outdoor non-yellowing varnish like Dura Clear by Deco Art. Using a varnish suitable for outdoors will protect your floorcloth from wet and muddy feet and will easily wipe clean with a damp cloth. For the sake of safety consider painting the back of your floorcloth with Fiber-Lok Non Skid Backing!