Hello Mary. Thank you for contacting us with your question.  It just so happens that I'm dealing with the very same issue.  I have lots of bad things to say about bermuda grass. Lol.  Anyway, you are on the right track.  We scalped the grass right down to the nub.  My husband has a propane flame thing and he burnt what was left, however I'm not sure that part was necessary, but he had fun doing it.  We then laid carboard, making sure there were no areas that would let any light penetrate.  If the cardboard was thin, we laid more over it. We then mulched heavily since we weren't going to plant anything in it this season.  It truly worked! If planting a garden, I would:

1. clear as much grass as possible. Right down to the ground with a weedeater if necessary.

2. Lay cardboard, thickly, and wet thoroughly.

3. Bring in topsoil and top with good compost. 

4. Plant.  No need to wait.  

You will still have some weeds and after a time that bermuda will try and rear its ugly head, but if you stay after it, eventually it will give up.   

Please let us know how it goes.  Thank you again for contacting Denton county Master Gardeners.

Judy Allen

Mary, I also wanted to add to my previous email.  I would use a generous layer of top soil (5-6 inches).  2-3 inches of compost. I always recommend a soil test, so that would be an additional option.  Once you have planted your plants, mulch with straw or wood chips that arent treated with any herbicides.  Can't wait to see your progress.   Judy