It really depends of how "correct"/"good" your work needs to be.
I have done a lot of interiors/architecture photos for architects portfolios and nothing can replace the PC ones.
They are expensive for sure. Even some times nothing replaces large format...
So if you are in a budget the new 20mm f1.8 is very good, but be prepared for some time on PS. One thing that most don't realize, is the PS corrections are, at the end, not any more real... because you loose the right perspective dimensions. Bt they are pleasing to the eye, thought.
So, for me, the only way to reproduce the best you can, and see, is like Akira said, pano stitching...
Either way a tripod, with a pano head, is always a most.