Usually the hardest part of repairing a leak is finding a leak. After a couple of days of dry weather, go around the outside of your greenhouse with a garden hose. Start at the bottom and have someone inside to look for water. Go all the way up to the top and pay special attention to places where 2 types of construction meet, like the greenhouse and the rest of the house. Remember that water can travel along anything that slopes, so even if you find where water may be getting in, look higher to see if you can find other likely spots.