Built a sliding barn-door in similar fashion, but clad in galvy steel (cheaper) Track made from 3 inch angle, home-brewed wheels running on edge of vertical side of angle (could use channel) door suspended by studding drilled down through top box- section.
Problem with horizontal -split bi-fold, you are needing pillars and roof truss to support the entire door weight....a counterbalance would double this, can be mostly mitigated by using a pair of long coil springs in torsion. Consider conventionally mounted hinged doors, can be split into sections to reduce windage......top and bottom bolts easily arranged with as deep engagement in frame and ground as your paranoia demands.horizontal braces can be slid through eyes welded to frames. For added protection, a beam can be mounted through eyes and padlocked.....mounted at Landrover windscreen- height, it'll take the roof off lesser vehicles that attempt a ramraid....4x4 vehicles tend to get abandoned (well, the remnants
) at the scene.
Of course, you could make similar secondary fortification with an up n' over bi-fold. Certain elements on the fringes of society will spy out before attacking, make it an easy choice for them.....breaking in to yours is too much trouble, there are easier pickings.........Mate had his garage broken into, via the only part of the asbestos roof that wasn't underdrawn with shuttering-ply or Weldmesh concrete-reinforcement. Once in, he couldn't climb back out, couldn't break out! rat in a trap! police sent dog in to flush him out.
O h, forgot to add....use a MIG welder....plenty of used ones about, far less skill needed than stick, friendly pub will supply co2 bottle refills for under a tenner!