The paper considers optical packet switching networks with slotted operation. A general model of network nodes is introduced, based upon a nonblocking switching fabric, and re-circulating fiber delay lines to solve contentions. Given the current large bandwidth availability in optical networks, and the projected limitations of electronic switches, a new approach to network design is proposed, aiming at balancing wavelength and buffer allocation taking the number of switch ports as a constraint. Given the problem complexity, a heuristic solution is proposed, using simple queuing theory to model network links. The effectiveness of the new network dimensioning approach is demonstrated by running a simulation program on manually dimensioned topologies, and on topologies dimensioned using the proposed approach.