There are two basic types of trailers utility and enclosed. Flatbed trailers offer a very popular entry level towing option they come in a variety of sizes from 4′ to 8.5′ wide and up to 32′ long. The most popular sizes are 10′ or 12′ long and 5′ wide. With a flatbed trailer you can load up your ATV for a day in the mud or carry plywood and lumber for a construction site. They are inexpensive and it is easy to get around to your tools and toys. You can even get basic protection from the rain with a tarp. Many utility trailers will come with a simple ramp to help with loading of cargo.
Enclosed Trailers offer a significant step up in protection and utility for a little more money. Your cargo can now be secure from prying eyes and the elements and you can even turn them into a mobile office or garage. Rear ramps will come with a spring assist to make opening and closing the door a breeze. Enclosed trailers are very popular with general contractors by allowing you to keep your tools and supplies at the job site while still having the use of the truck. There are many important construction features to look for when shopping for a new trailer. A good YouTube video that goes through some of them is here: