If you know houshold finishes you probably have seen the stippled finish on some interior paints in a house.
I did this in my cat. You need to smooth the surface first and here it just depends how neat a finished surface you want. The more effort you put in the better te finish will be. You can use any epoxy fillers to smooth holes etc but you can also use normal car type body fillers. Once you have the smooth finish you want you paint the surface with a paint called "stipplex" not sure what it might be called in your country but most house paint suppliers will have something like it. It is a very thich water based pva paint which is applied with a sponge type roller which has large holes in it. This will give a stippled base coat, If it is too rough in places you can very lightly sand over till you are happy with the texture. After it is dry you can apply a final coat of acrylic interior/ exterior paint (ask for a good quality paint that can be wiped down if dirty). I used a produt called velvaglo which is advertised as being good for bathroom walls etc were you have a high moisture content or steam.
This is a relatively cheap way of doing it and gives a good finish, it just depends on your prep of the bottom surface.