It's totally normal. Carpet comes on rolls in widths from 11'6" to 13'. They need to cut off a chunk of that roll to fit the room.
It's the reason why if you're carpeting a 10x10' room, you can't buy 100sqft of carpet: they'll charge you for more like 120sqft (12' roll, 10' long).
It also depends on the layout of the room, and where they put seams (if necessary). Eg: an L-shaped room has a couple different ways to lay out the carpet, and depending the layout and where the seams are, you'll use a different amount.
A good installer will also consider traffic: if there are seams, you don't want them right in front of a door way, or preferably not running down the middle of a high traffic pathway. I think they also avoid putting seams within a foot or so of walls (so there isn't a narrow strip of carpet running along the wall). All of these things may end up using more carpet than a layout optimized just to minimize scrap, but will result in a much better looking and longer lasting install.
The other factor is in patterned carpets, they will use a bit more since the patterns need to line up. The bigger the pattern, the more is scrap needed to keep it in line.
The important bit is to keep the scrap carpet, unless you really don't need it, since you
paid for it. Often there is a good size chunk, which can be used for many things:
Carpet will be cheaper to have installed, but the life time is much shorter than hardwood.
Look into strand bamboo. I believe it is much harder than any other hardwood and not as susceptible to humidity. I used it in my house on the most of the main level (about 1,500 square feet) and have been very happy with it.
Because it so hard, it is more difficult to install, so you may pay a little more for installation.
I don't know if you can ever avoid all creaks, but most can be avoided by putting down rosin paper first and nailing into the floor joists as much as possible.
UPDATE 1
I'm talking specifically about strand bamboo. Regular bamboo is much softer and scratches a lot easier.
Best Answer
If the builder is giving you the option and he has the material, I'd go for it. After all the work is done, the last thing you want to do is rip out the stairs and put in new ones. Carpet on stairs takes a beating especially on the edge and vacuuming them is a pain. Sure, it will cost more (much more) than a DIY project but it will be money well spent.