construction drawings for a used concession trailer

I have a question that i have looked all over for the answer with no luck. My health fepartment wants construction drawing for this trailer and i do not have them or do i want to spend a ton of money on. Is this something i can do myself maybe on graph paper. I even see that there are free blueprint sites where i think i can just put in measurements but im not sure if health department wants a professinal to do it. I called a bunch of architects only one answered said he couldnt help me. Please let me know what you did for your drawings if you had a similar dilemma.