Hybrid precoding architectures can address the trade-off between achievable spectral efficiency and power consumption in large-scale MIMO systems. Most of the prior work on hybrid precoding focused on narrowband channels and assumed fully-connected hybrid architectures. In this paper, a closed-form solution for OFDM-based wideband hybrid precoding is developed for both fully-connected and subarray architectures in frequency selective channels. The closed form solution provides useful insights into how hybrid subarray structures should be designed. Based on that, we propose a novel technique that dynamically constructs the hybrid subarrays based on the long-term channel characteristics.