For example, he estimated four hurricane impact-resistant windows and a garage door would cost between $4,000 to $5,000. But after multiple quotes from contractors, he ended up paying $9,800.

More from Personal Finance:
The tax deadline for American expats is June 17
Home equity is near a record high. Tapping it may be tricky
What to expect from the housing market this year

Since their mid-April home purchase, the couple also hired contractors to refinish their scratched-up wood floors for a total $2,200; installed a pool safety fence for $1,673; removed popcorn finishing from the garage ceiling for $800; had someone prime and paint ceiling texture for $650; and replaced cracked roof tiles for $1,670.

“We’re still kind of anticipating more expenses,” said Marrero, 33. “I know the pool pump is on its last leg. So, we’re bracing.”

Marrero’s experience isn’t unique.

Experts say the “hidden costs” of owning a home, especially repairs and maintenance, can come as a shock for homeowners.

Roughly 1 in 5 (19%) of homeowners found the cost of home improvement projects to be the most surprising element in the first six months of homeownership, according to a new report by Angi.com, an online marketplace that connects homeowners with professional contractors for home maintenance or renovations. In late May, the site polled a total of 1,000 Americans who bought a home in the past five years. 

“Living in an apartment, they’re likely not hiring home improvement contractors, so I think there’s kind of the realization of just, how much does it cost to hire a plumber,” said Angie Hicks, co-founder of Angi.

“Understanding that process is enlightening for them,” she said.

Annual “hidden costs” of homeownership average around $18,0000 nationwide, according to a separate report by Bankrate.com. Its report estimated home maintenance at 2% a year of the value of a home.

Based on that calculation, Bankrate estimated, annual maintenance costs in some of the states with the highest home prices — like California, Hawaii and Massachusetts — can go over $26,000 annually.

Meanwhile, in Kentucky, which Bankrate pointed to as the least expensive state, annual maintenance might be around $5,000.

First-time homeowners are less likely to be aware of those costs than those who have previously owned a home, Angi.com found, and more likely to say they spent more than expected on home maintenance, improvements and emergencies.

“Once you’ve been a homeowner for a while, you realize everything that can go wrong,” Jeff Ostrowski, an analyst at Bankrate.com, recently told CNBC. 

Here are things you should consider when shopping for a home and as a new homeowner, to help limit maintenance surprises:

In April, around 19% of buyers waived the home inspection, down from 22% one month prior and 21% a year earlier, according to the National Association of Realtors.

Sometimes home inspections are skipped because they have to be done in a quick time frame and “you start to make choices that may be ideal” out of the fear you’ll lose the home, Hicks said.

But hiring a home inspector is essential, said Dan Bawden, a residential construction expert and president of Legal Eagle Contractors, Co. in Bellaire, Texas.

“That’s probably the most important thing you can do,” he said.

Typically, home inspectors need one week’s notice on average, he said, so keep that in mind as you start looking at homes.

Ask real estate agents for referrals on licensed home inspectors in your area who will conduct a thorough service, Bawden said.

“Instead of spending $450, you might spend $600 for somebody that’s better, but that’s money well spent,” he said. “You want them to find as many things as possible.”

The home inspection is “an important element” in the home buying process because you can discover elements in a house that could be a “deal breaker,” said Hicks.

Be present for the inspection, if you can.

“If you’re there with them, they will tell you what things are urgent or severe,” Bawden said.

For instance, if the house has many cracks along the door way or windows, or feel a downward slope as you walk across a floor, it may have foundational issues, he said.

“You do not want to buy a house with foundation problems. They will get worse over time and they are expensive to fix,” Bawden said.

Other notable deal breakers include termite damage and water damage, he explained.

An inspection can also help you understand the age of important elements, like the roof. Take advantage of the inspection process to ask questions about these elements, and then assess if you have the budget to cover those costs, or if it’s something worth asking the seller about, Hicks explained.

Having a complete list of problem areas noted in an inspection can help you prioritize repairs and potentially negotiate the purchase price of the home, said Bawden.

Once you become a homeowner, it will be important to keep up with routine maintenance in your house. “Don’t skip out on having that air conditioner or furnace tuned up,” said Hicks. “It’s like changing the oil on your car.”

To avoid surprises, try to regularly inspect your home and look for spots or corners that may need to be fixed. While homeowners are “the most critical” of a house when they’re buying, they often don’t keep the “critical eye” after moving in, said Hicks.

Have mechanical system check-ups at least once a year, said Bowden, as well as plumbing and electrical system check-ups.

“You need to be vigilant,” he said.