In reply to Sonjita:
There are pro's and con's to whichever rope you buy.
I would suggest that you get a single rope (as has already been suggested) and also a dry treated rope. If you get caught out and it rains, you don't want your rope to get heavier.
In addition if you end up getting into winter climbing, a dry rope won't freeze as easiliy as a normal rope.
(basically you pay for what you get)
50 meter or 60 meter it really is upto you. traditionally ropes started as 45 meters (my first half rope was one of these), but routes get longer and on muti-pitch routes it means that you haver to belay less frequently.
A 60 meter rope means you can abseil further
to summarise the length of rope is upto you but 60 meters are becoming the norm.
I would buy a rope from a know source. I have seen the full rope that I am about to retire on Ebay. (ropes stored in a dark room still degrade) so what is being sold as a new rope is in reality old but just unsed.
I hope this make sense
Richard