The image below references different sizes and shapes of canvasses I typically use. A common door is included for comparison.
Flat panel or stretched canvas? Flat panels are less expensive and easier to ship. They require a frame to mount on a wall or place on a desk. Stretched canvas is stretched over a timber frame that is 1.5 inches (3.8 cm) thick, with mitred joints. It can be mounted on a wall without a frame, but has higher shipping costs.
Oil or acrylic? Oil paintings require more time to dry before they can be varnished and shipped. Oil is only a viable option if you do not require quick turn-around times. It can take many months for oil-based paints to dry. Acrylics dry very quickly so acrylic-based paintings can be shipped much sooner than an oil painting. Whether you prefer the look of oil or acrylic is subjective and personal. I love working with both mediums because they both produce beautiful paintings!
Solid colour, natural environment, or something else? Solid colour backgrounds make your subject pop and are quicker for me to paint, reducing the price. Natural environment backgrounds include realistic settings, but require more detailed brush work and time. Reference photos for natural backgrounds are very helpful if you are keen on including that in the painting. I also enjoy creating backgrounds that are unique, so if that interests you I am happy to chat about ideas.
A dog, a cat, a bird, a person.. or something else? One subject or more than one? Reference photos for each subject are very helpful.