Hi 'Chrome,
I put the carpet up in one piece.
I think I cut it roughly to shape due to the sloping ceiling, then pasted it before hanging it up. I had already pre-pasted the wall earlier so there was plenty of glue. My other half helped with it of course, otherwise it would have been very tricky.
I then trimmed the edges with a stanley knife (new blade) and used a roller to ensure it was all in contact with the wall. There is some far blacker carpet out there now, but at the time, I couldn't get any that jet black and reasonably priced.
The carpet was a thin rubber backed chargcoal black form Carpet Right - it was about £1.99 a square ft IIRC (about £20), so it didn't cost much. All the grey carpet I used on the side walls cost me just £50 or £60, so I'd carpeted the walls for well under £100. The floor carpet wasn't expensive either, and I laid the underlay, gripper rods myself and fitted it too. It's easier than you think.
Gary.