There are many professionals in this thread and Im not one of them. The professionals in this thread from what I have read in the past, dont live in the south. Their budgets and percentages are crazy compared to what stuff costs here in TX. Being that you are in OK, your budget is plenty. Builders around here can build a tract home for $60/ft. Semi custom homes with a builder are $90-100/ft. I know a builder (personally) that builds in a TX that builds his custom houses for $75/ft (his price..not sales price). I would just go with a draftsman. Dont listen to the "double your budget or half your house). This isnt the northeast where a normal house is $200/sqft. There was a great thread a while back on a TX house being built for $65/ft self contracted. Oh, and metal roof isnt THAT expensive. I put a new roof on my own house (my dad and I did it). 40sq of roof from Mueller with all the trim (r panel roof) in galvalume was $3200 for materials. The sales guy said it would be about 15% more for standing seam. I got a quote to install the roof and it was $4000 for install. That being said, a dimensional shingle roof was $10k with tear off and haul away.

It's a pretty layout! But how much space is there between the sofa and chair? Or the sofa and loveseat? You want enough room to walk between them and get to the sofa....or past the chair to the master suite. I would suggest graph paper and cut out some templates....or use a software program. And make sure you measure the DEPTH of sofa, loveseat, chairs, etc. So many of these designer programs seem to have sofas that are less than 3' deep. Most are more like 3 1/2'. Take accurate measurements of your proposed space and move the pieces around. Then measure your walkways now and see what works and what might be too narrow. It would also be a good idea to measure you dining room and try different tables and see if you have space for chairs to pull out, etc. And you might visit the Home Decorating forum. They have good ideas, too :)

This is a long and positive thread trying to help the OP as much as possible. The OP really needs some experienced and expert local help. There is so much that needs to be explored and evaluated, starting with the basic concept of the cost of having a basement, which, by definition, will not likely be accessible to a child with limited mobility and special needs. As helpful as everyone wants to be on this forum, no one is going to be able to work out a good concept and design, except for a direct, on-site presence with the OP and family. As a former Head of a school of architecture and tenured full professor, I have to say that contacting a university school of architecture is probably not a very good strategy, unless that school has an organized, staffed and functioning community outreach and assistance program. Some universities do; many do not. Most faculty members plan their course-work a semester or year ahead, and focus on teaching a number of cumulative design principles to the students, year by year. As important as this project is, it probably doesn't fit well into an architectural curriculum, unless there is an active community outreach program, as I've mentioned. It's possible, that the nearest local chapter of The American Institute of Architects might sponsor a charette or even a pro bono program of support if contacted with details about the situation. My heart aches that so much help is needed here.

Post this as a poll and you'll see Houzzers vote for an architect. However, it may depend on how substantial the renovation is and what things like plumbing and vents may need to move. Some architects won't take small jobs. Some draftsmen don't have the skills needed for some jobs. Get references locally for both and see their work.