There is always a Group Build active, each one running for four months, with an overlap in between of one month. The current GB (Heavy Hitters II) commenced on May 1st, and will end on August 31st, with the next GB commencing on July 1st.
All GBs prior to this are now ended, and closed.
The full listings of forthcoming GBs, and the Rules and Photo Requirements, can be found in the GB section of the Modelling threads. Have a look at these and then, if there are any questions, post them in the GB Modelling section.