I took one of the generic internet ones, copy and pasted it to a word document, then started editing. I deleted all that didn't apply (there was a lot) and then started adding my own items. I had a rule that the SECOND I thought of something, I'd stop what I was doing, and go add it to the list. I did this for a month leading up to picking up my new rig. The real hard part is remembering to check everything you have on your list while all the excitement of the delivery is going on. I had to force myself to calm down and follow the list and I still skipped a few things...
I've used the Tom Boles' Pre-Delivery Checklist from this site I think the only thing missing on it is to bring a 5 gallon gas can. Enough to empty into the tank and then dispense back into the can to make sure the fuel station is working.
If others have a more specific Toy Hauler PDI please share with the group.