In Mark Twain’s classic The Adventures of Tom Sawyer, Tom tricks his friends into white washing his aunt’s fence. You probably won’t get that lucky, but there are good reasons why many homeowners keep their painting in-house: No building codes apply to interior decoration; if you do something dumb, you don’t risk life and property as you would if you were, say, tackling a rewiring job; and since labor typically accounts for 80 to 85 percent of the price of any paint job, you’ll save a ton by grabbing a brush.

Before taking the painting plunge, consider the following:

Inside or outside?

Inside there are solid floors, reachable ceilings, and uniformly bright working light. Outside, uneven ground makes it difficult to set ladders and reach roof overhangs. Nature isn’t your friend here either: Morning dew that can cause paint adhesion problems and storms can ruin still-wet paint.

One room or the whole house?

Applying one coat in one room is a reasonable DIY Saturday project (especially if you have help and beer). Multiply the time spent moving furniture, prepping walls, and sanding old trim by the number of rooms in the house and you might want to hire guys in painter’s overalls. It’s the same outside. You can probably tackle one shady garage wall that needs a little scraping and sanding plus a coat of paint, but covering all surfaces of the house is usually best left to a pro.

One or two stories?

Painting one story may be within the scope of a DIYer. Two stories means extension ladders and scaffolding—probably contractor territory.

New work or repair?

If a remodeling contractor leaves smoothly finished drywall, prep work is eliminated and the painting can begin. Where walls or siding need a lot of scraping, spackling, and sanding, the same-size project can take twice as long.

Same color or stark change?

Repainting with a similar color rarely requires more than spot priming and one finish coat. Dramatically changing the color usually requires at least two coats, doubles the painting work, and generally necessitates extra time for drying.

Mostly walls or woodwork?

A roller makes quick work of unobstructed walls. Rooms with wide baseboards, elaborate window casings, and cornice molding at the ceiling demand more time and effort. A lot of trim means a lot of brushwork—even more so if the job includes cabinets and shelves—and edges into the realm of professionals.

First-rate or second-best?

Take a look at painting projects you’ve tackled in the past. Is the trim as smooth as you would like it to be on the new project? Are the walls uniform and free of lap marks? If you want results that may be difficult and time-consuming to achieve by yourself, hire a good contractor.