In Washington, if you build or buy a homemade trailer, you must provide original receipts for all major parts in order to get a title. If you don't have them, you can get plates, but have to wait 3 years to get title.
http://www.wsp.wa.gov/traveler/docs/cvd/170_129.pdf
Bruce
so just out of curiosity, what's the downside of not having receipts? if you can still get plates and use it, why care about a 3 year wait for the title? i've had 5 trailers so far in my life - 3 homemade, 1 manufactured bought used, and one manufactured bought new. in my state they don't even title a new trailer unless the empty weight is over 3000 lbs.
homemade is just your word at the local town office and then whether it has multiple axles to determine the fee. new or used manufactured (under 3k weight) just wants a bill of sale with a vin on it, and proof that you paid state sales tax on the purchase price.