I can't really recommend anywhere, i'm from the U.K. I know Newegg is a reliable place to buy components though.
Building a PC yourself isn't that hard, just try watching a few videos and reading a few guides and you can really save yourself a lot of money. The only realistic ways to break something are:
- Bending CPU pins, but you would have to be very heavy handed to do that.
- Killing something with a static charge, just buy an anti static band and that won't happen. Try to keep static sensitive things away from carpets/fabrics too but don't worry too much about it. My GPU was sat on my bed for a bit a few times and that works fine.
- Something short circuiting or overheating because it's not screwed in properly. This one is self explanatory, just make sure everything is screwed or clipped in before you turn anything on.
That's really all there is to it, just read a few guides and you will be fine.