What size SSD would suffice for basic software-development / productivity? My friend is selling me his old MacBook (Glossy white finish with rounded edges and corners) cheap for a Mobile Development course I'm taking, but he's keeping the hard drive. So I'm thinking of buying an SSD off of somebody, and I'm not sure what the minimum size I would need.

I will have to install:


Either keep Snow Leopard or Lion
Xcode
Whatever is needed to develop for Android and iOS
Possibly some form of productivity suite (MSO or LibreOffice)


I barely have any experiences with Macs so I'm not sure how much space all of this would take up? I need to have a feel for the smallest SSD I can get
A 128GB SSD would have enough room for what you list, with room to spare. A 256GB SSD, imho, would not cost that much more, and would give you more flexibility. 

Be aware that the version of Xcode needed to develop for iOS 7 requires Mountain Lion, and ML may not support that machine. For learning or developing for iOS 6, Lion/Xcode 4 should be fine.