We're just going now through the process of building a new house. Land is around 10% of the overall budget (and this is a really sought after area in CA).

We did a lot of research and we were initially thinking of prefab for our home, but we finally decided to go for full custom design. In the end, prefab can really make some costs more predictable, at the cost of some flexibility in the design. Cost-wise, it was almost the same (for our case) but construction would've been faster and more probably more controlled in terms of budget.