Just some advise for those thinking about building. If you are thinking about covering with aluminium check out alucobond which is basically two thin sheets of aluminium sandwiched between a composite material. These sheets come coloured so there is no need to spray paint. Unless you can get your sheeting at a good price it mite just be worth using alucobond as you don't have to paint it. When building a trailer of a reasonable size the cost of paint can be very high especially if painting inside as well. I decided to go with aluminium sheeting and spraying my trailer as I got the sheets at a reasonable price.