In reply to George Fisher:
My advice would be that for architectural interiors, you want minimal distortion, (unless for whatever reason, you're not bothered by that.) In which case, I'd probably stay cropped sensor format and get a wide angle such as the Tokina 11-16mm f/2.8 which is fast and sharp. No point in splashing cash for full frame , giving you wider images, but which will consequently be more distorted.
Of course, I might be talking rubbish and no doubt someone more qualified (of whom there are many on this site / forum alone) will come along with better and more appropriate advice
Best of luck.