It can be a very good way to make money, but how easy it is depends on how much you can start off with, the type of house you have in mind and the buyers you are marketing to.
You can shop around for a lender that will provide the money, similar to a construction loan, or even a line of credit, like a builder, for the houses. What you may have trouble with is the fact that it will be non-owner occupied, which will raise the rate, and come with a strict set of guidelines. Not all lenders will do it. I think this will be difficult, but that isn't the type of lending I do. There is always a lender for whatever you want, they may just be hard to find. Maybe someone will chime in with an idea. If you purchase the house and use your own money for the upgrades, you may have to be ready for 10-20% down. Plus, a higher rate than owner occupied property. Best bet might be a small, local bank where you can establish a relationship. A new bank if possible.
Do this ONLY if you find a GREAT buy on a house. Don't count on HUD homes, HUD will not do any repairs on the house, as a matter of policy. And they usually need it. If you don't get a house that you can make a good profit on, you might end up eating it from the interest you pay while trying to sell. Start slowly, learn the market.
Some lenders have gotten to the point where they will require the house to have been in your name for _____ months to a year before they will close a loan on that property. The reason for this is "flipping". A person can do what you are talking about, get in bed with a shady appraiser and buy a worthless appraisal with an inflated value. You can't just slap a coat of paint on a house to make it look good in a picture and all of a sudden make an extra 30% on the house. It all comes around. You sell the house for more than it is really worth, and then the person is upside down in the house. They find out when they try to sell later adn get an honest appraisal. They can't afford to sell. Often, the house ends up in foreclosure, the appraiser is in jail, and you could be next, or at least sued. If you do this, do it with houses that will attract strong borrowers in good neighborhoods. There are good buys out there that will let you do it right and make some really good money.
Don't go into this like some have, learning from some infomercial guru. Don't get into trying to sell houses that aren't yours, closing your purchase at the same time as your sale to keep from putting money down. That's BS and won't last long. Be careful what advice you get, but this can be done if you do your homework and keep track of the dollars and cents of what you're doing. Some people make really good money doing it, I know of a few guys that have been able to do it full time. They turn out some good houses and everybody wins.
*PS Don't even think about mobile homes.