Length
Line up your cooking equipment side by side, then add the prep counter, a hand sink, a dishwashing sink, refrigeration and storage. That total sets the length, not the number of items on your menu. Leave room for the people working inside, too.
Electric only, or propane
Coffee, ice cream and cold food can run on electricity alone. Fryers, griddles and burners usually need an exhaust hood and a fire suppression system, whether they run on electricity or propane. A propane trailer also needs TSSA approval before it can be used.
Power
Add up the wattage of your electric equipment and the air conditioning, and note which of them run at the same time. That decides the size of the power inlet, and of the generator you'll need where there is no hook-up.
Water
You need a fresh water tank and a separate grey water tank, sized for a full day of service. The grey tank is usually the larger of the two.
Where customers stand
Decide where the serving window goes. It is normally on the curb side, so customers stay off the road, and the cooking line is planned around it.
When you have your answers, see the trailers we build or price your own build.