Disk Space requirement for Xcode on a Solid State Drive (SSD)

Question

I have a question on the storage requirement for running Xcode and working on Application development.

I am planning on upgrading my Macbook Hard disk to a Solid State Drive (SSD) for an increase in speed. Would it be enough if I have a 128GB SSD , or should I go for the 256GB SSD (which is more expensive) ? Could anyone help me with this ?

Thanks.