If he knows he will get the death penalty, he thinks he may as well use the trial as a platform for his twisted agenda.
My guess is that he when the trial does come, Roof will not be acting as his own attorney.
That wouldn’t be surprising-there have been a few cases of criminals who are psychos acting as their own attorneys until they figure out they have sent the trip to death row into warp drive-then they suddenly want an attorney appointed for them...