Walk around the barn and look for any evidence of water such as moisture, water stains or rotting wood. Inspect the inside of the building. Look in all the dark corners and clean out any old hay, animal droppings and dirt so you can see the damage. Stick a penknife into the wood to see if there's any rotting under the paint.
Make a list of your findings and craft a plan. If there's structural, foundation or roof damage, decide if you're going to do it yourself or hire a contractor.
Repair or replace roof first. For small repair jobs match the material on the roof, but when replacing the entire roof, pick between slate, shingles or metal roofing. Match the flashing (pieces of metal that goes around pipes or other objects sticking out of the roof) on the roof with the roofing material, because improper flashing causes most roof leaks. Replace any rotten boards on or around the edge.
Check foundation for signs of water. Poor drainage and frost heaving are the main cause of foundation problems. Slope the soil around the foundation so the water goes away from the barn. Repair cracks by filling them with mortar. Numerous cracks and damage may require jacking up the barn and installing a new foundation. Install new concrete walls five to six feet below frost level.
Examine the frame piece by piece, include timbers, joints, cracks and support poles. Replace any timbers that show signs of rot or insect damage. Add wire cables for additional braces to support frames. Repair timber, not part of the support system, by filling the cracks with epoxy and wood filler. Replace any rotten boards on second floor. Intensive damage to the frame may require the barn being jacked up and the frame replaced.
Replace any broken glass on the windows. Check window and door frames and replace any rotted wood. Aluminum windows are good replacements for windows with rotted frames. Clean and repair sliding tracks for doors. Remove rusty hinges and latches and replace with new ones.
Scrape loose paint chips from the outside of barn before painting. Pick a durable outdoors paint. Spray, roll or hand brush the paint on the outside of the barn. Brush painting gives the best result but is time consuming. Paint doors and windows with an outdoor trim enamel.