If you have a general idea of the design you want, maybe head over to Ana White.com and ask someone on the forums to help draw up a building plan. If you explain what its for, I'm sure somebody will jump at the chance to help.

I am wondering how you went about trying to get the insurance company to pay for it. I manage a durable medical company and we have gotten them covered. It is all in how the physical therapist writes up the LMN or letter of medical necessity. If this is not done correctly you will get a denial. It has to be written to say the child is not safe and the bed is required to ensure safety at night. We also get full sized strollers approved because ASD children tend to elope. We get them covered even though the child can fully walk and run. Medicaid should cover either of these items but again it is all in the paperwork.

If you did go through a DME I would reccomend using one of the bigger national ones and not a small local because they often do not have experience with specialty products.

If you have the space, a trampoline with the net enclosure is a dual function, expel energy in the day, and with a pad formed to fit holds the kiddos safe at sleep time.

Are you looking to build a bed with high side rails for safety or a semi-enclosed bed to give your child a hidey-hole?
I built bunk beds for my kids - there are pictures on my pinboard. I figured they would fight over the top bunk but no. They both want the bottom bunk because it's semi-enclosed and they love it.
If you can give me a little better idea of what your going for, I might be able to give you some ideas.