Assess the items that need to be stored to determine the amount of storage space needed. A larger storage loft is more costly and takes longer to build than a smaller one.
Climb up the ladder for a clear view of the rafters and joists. Pole barn rafters are the diagonal boards that run up the ceiling and form a peak at the top. Joists are the horizontal boards that run from rafter to rafter, across the open space under the peak.
Measure a space from joist to joist, or across multiple joists, that is long enough and wide enough for your storage needs.
Cut pieces of plywood to lay over the joists in the area that you measured. Use the largest pieces of plywood possible to cover the space. Each piece of plywood must begin and end on a joist so that it can be nailed to the joist for stability.
Lay the first piece of plywood. Slide the plywood into place so that both of its ends rest on joists.
Nail the plywood to the joists using four nails, one at each corner.
Lay the other pieces of plywood until the storage space is covered.