We consider the problem of physical-layer network coding when the channel exhibits block fading. Specifically, we focus on the use of lattice codes in a compute-and-forward framework for realizing physical-layer network coding. We construct a novel lattice ensemble called the root-Low-Density Construction-A (root-LDA) ensemble which uses Construction A with root-low-density parity check (LDPC) codes. Using extensive simulations, we show that the proposed lattice codes exhibit full diversity when used over the block fading channels. In addition, their performance is comparable to the performance of LDA lattice codes optimized by the progressive edge growth algorithm over the additive white Gaussian noise AWGN channel. This suggests that root-LDA lattice codes provide a robust solution to the problem of implementing physical layer network coding over fading channels.