Maybe not steam powered, but pulled by an ochs.
Could require same resources as cart + metal plow + a bit more and would have a container where you can dump stones into (like feeding trough).
When filled you can mount is and drive like with waggon to lay a road.
LP gived would have to be way lower than doing the same manually (or even give no LP at all) since it would be a convenient quick way to build roads.