To accomplish what you suggest is quite possible, especially in CA where many fabricators make good livings by modifying vehicles. Because it will be a complex undertaking, the costs involved will be substantial. The fiberglass roof is supported by metal supporting structures. The additional height added to the walls, will have to be reinforced to support these braces. The fiberglass roof is a singular one piece design, and will have to be removed and replaced intact. Have you considered how to treat the additional heights above the doors? With a horse growing as large as your's potential, it might be advised to add an additional height to reach 8' instead of 7 1/2'+. This should not be a first time job offered to someone who thinks he can do the work. This will take skill, adequate tooling and facilities to properly complete. If it is done incorrectly, your trailer will be ruined. I would seriously consider the purchase of another trailer. This would be a major fabrication and expense, and may not work out well. Gard | 
Raising trailer roof
