How to pronounce "wadaya gonna do" correctly in American oral English (phonetic spelling), and do you need to roll your tongue for the weak pronunciation of "A" of are?

What are you going to do？

When you say a, you usually say it with cha, without rolling your tongue. What Wa cha has to do is to read the first word in two parts, and A doesn't read it alone.

Please take the following songs for reference.

Bad boy, bad boy, what will you do when they come to you?