If you’re the handy type, buying a fixer-upper can be a challenging, gratifying, and all-around fun experience. But even if you consider yourself a master of all things DIY, there are certain homes that are going to be a drain on your finances—and just aren’t worth fixing up.

A recent article from a personal finance resource Money Crashers outlined the warning signs a fixer-upper might actually be a money pit. Some of the biggest red flags to look for include:

The smell of moisture. Moisture can not only cause structural damage to the home, but it can also promote the growth of mold—and make it completely uninhabitable. If you can smell moisture, consider it a major red flag.

Sloping or sagging floors. If the floors of a house are warped, it’s an indicator of structural problems.

A bad roof. Repairing or replacing a roof is an expensive undertaking. So, if a property’s roof is about ready to give and nothing can be negotiated, it’s probably a good idea to move on.

Foundation issues. It doesn’t matter how well you fix up a house—if it’s built on a faulty foundation, you’re going to run into serious (and expensive) issues down the road.

Bottom line? Fixer-uppers can be a fun and potentially profitable challenge—but if you’re dealing with a house with serious structural damage, that fun challenge can quickly turn into an expensive nightmare. Make sure to use the help of Realtors and Home Inspectors to insure you don't end up with any surprises when buying a fixer-upper.