One side of the H is 10' x 2.5 ft = 25 sq ft. Other side of H is the same = 25 sq ft.
H is total 10 ft wide, minus the 2.5 ft, minus 2.5 ft makes the H "bar" 5 ft long by 2.5 ft. wide = 12.5 sq ft.
12.5 + 25 + 25 = 62.5 sq ft. (takes a lot of plywood) 3-- 4 ft x 8 ft sheets of plywood.
Might want to consider 8 ft high x 8 ft wide using 2 ft thick block letters. Comes out looking about the same ratio, and would only take 2 sheets of plywood. Generally can legally haul 8 ft wide preassembleld " H" on a truck, but not 10 ft wide "H".