You might find that spending a little time and effort upgrading your 1/4 mile path, potentially even building some small bridges for the water hazards, pays large benefits in the ease of hauling materials to your building site. You could probably also customize a wheelbarrow for the panel-carrying job - ideally starting with one that needs a new pan, or else starting with a (sturdy) bicycle wheel and making it from the ground up. To carry a 4x8 foot panel effectively you want handles nearly 6 feet long, so you may need to go custom anyway. The panel can overhang the wheel a bit, but the center of the panel needs to be on the same side as the handles, and you need enough room to hold the handles and not hit your face on the panels.
I will share that single-wheel wheelbarrows are much better on a non-level (side to side) path than two-wheel versions, as you can hold the single-wheel type upright, while the two-wheel cart follows any tilt in the path, and can be more prone to tip over as a result. You should also beware of the urge to load as much as you can pick up into a wheelbarrow - it gets heavy on a 1/4 mile trip, and then you may end up dumping it before you reach the end.