Replacing a roof is pretty costly. You can expect to pay anywhere from $4 to $7 per square foot for asphalt shingles and even more for specialty roofing materials like slate tiles or metal sheeting. So if you're thinking of purchasing a property for sale, it really pays to ensure the roof is in good shape first. Otherwise, you might find yourself paying thousands in repair costs just a year or two down the road.

Here are a few things you can look for to get an idea of the condition a home's roof is in.

Clear gutters.

Take a look inside the gutters. Are they clear, or is there water backed up in them due to leaf and debris accumulation? If the gutters are blocked, water will accumulate on the roof. If this has been happening for some time, it can cause the wooden roofing underlayment to begin rotting, which could actually lead to dangerous conditions like a sagging or a collapse-prone roof.

Lack of sagging.

Standing on the ground, try to angle yourself so that you're looking straight across the roof. Make sure you don't see any dips or divots. If you do see areas where the roof is sagging, you should probably move on and say "no thank you" to this home. A sagging roof is a huge project to fix and is at risk of collapse, so you really should not live in the home until the repairs are made.

Shingles in good condition.

Are the shingles peeling up at the corners? Are they starting to lose granules that are accumulating on the ground? If there are just a few peeling shingles, you can likely have them repaired or replaced and get a few more years out of the roof. However, if the majority of the shingles are peeling or you see a lot of peeling shingles on one area, the only option is likely to replace the roof -- and soon. The peeling can also indicate a lack of insulation or ventilation, which are also expensive issues you'd have to deal with upon moving in.

Solid flashing.

Look at the metal that surrounds the chimney and anything else that projects from the roof. It it's peeling or bent, then water is probably seeping in behind it and causing roof damage.

Unless you have thousands to dedicate to a roof replacement, it's generally best to avoid purchasing a home with a damaged roof.