Dont mean to poo-poo your project but, My high school shop teacher and his former school were involved in a lawsuit involving a runaway trailer causing a double fatality. I do not know the details but I believe it was operator error or coupler problem but the lawyers go after everybody.
He has not allowed a student to build a trailer in school since. coincidentally I am about to visit with with him this sat. morning.
Actually I am surprised that your school has the floor space available for such a project.
I highly recommend that you use engineer stamped plans for this.
I know schools are a great source to buy steel from due to the educational discounts.