Who was Missy (Misdemeanor) Elliot's Architect and Interior Designer's
for her home in Virginia?

Though I can't directly answer your question, I can tell you where you
might get your answer.  MTV runs a show called "MTV Cribs" which
highlights the homes of famous pop musicians.  MTV Cribs episode 301
features the home of Missy "Misdemeanor" Elliot, and may contain the
information you desire.  The next showing is Thursday, June 27th, at
2pm.

Though, I have a hunch that you may be wanting the information BECAUSE
you saw that episode of MTV Cribs.

I did some more searching and could find nothing else of interest.