Peter Rader, a screenwriter and sometime builder of one-of-a-kind play structures, peppers his speech with words like "magic" and "fantasy" — just what the lucky kids in his Nichols Canyon neighborhood want to hear.

Peter Rader, a screenwriter and sometime builder of one-of-a-kind play structures, peppers his speech with words like "magic" and "fantasy" — just what the lucky kids in his Nichols Canyon neighborhood want to hear.

For 8-year-old Ben Tzudiker, the fantasy was a treehouse — an elusive dream, considering his family's yard had limited space and no trees strong enough to support such a structure.

But Ben also was obsessed with the 1927 Buster Keaton silent film "The General," the story of a Confederate train engineer in pursuit of his beloved (a locomotive, naturally). After walking the property with Ben, Rader incorporated the two wishes into a single vision: a train-treehouse.

Set off the home's deck, the multilevel structure blends into the landscape. It is an enchanting place, where fantasy speeds along through Rader's unconventional use of ordinary hardware-store materials.

A suspension bridge connecting the deck to the train is made from lumber and heavy airplane cable. The door to the train is an attic vent. Galvanized sheet metal riveted with roofing vents forms the body of the train and serves as a tunnel to the "treehouse," a raised, free-standing structure built amid the trees but not actually in one. An oscillating roof exhaust fan, spray-painted black, simulates a smokestack. Corrugated metal siding paired with trellis panels give the three-story exterior a scrappy, hand-built look.

To finish it off, Rader connected a train store whistle to an air pump so Ben can blast real sound. Working headlights and a bell add to the sensory experience.

Rader, the son of an architect, fell into his secondary profession (www.fortsandfantasies.com) out of necessity. His children Matteo, 8, and Luca, 5, needed a place to play on the hillside lot where he lives with wife Paola Di Florio.

"Both my kids are not the kind of kids that would climb things or take physical risks," he says. "So I thought, why not create a structure where they feel embraced and safe?"

Rader started with a prosaic store-bought structure and elaborated with decking, a crow's nest and a captain's wheel. After adding a tower, his first hyphenated work, a pirate ship-castle, was born.

Blocks away, in the home of Linda and Angus Wall, Rader created a pirate ship for sons Quinn, 8, and Jake, 4.

The boys were specific, Rader says. They initially wanted a pirate ship, but as construction unfolded, their fantasy became a 45-foot-long half-pipe for skateboarding.

"What makes me excited about building these is the kids requested these structures," Rader says. "They specifically described them to me. I want the kids to feel like they contributed."

Seeing children having fun is satisfying and thrilling.

"These years, when kids are little, are so precious," he says. "They have a job just like we do, and their job is to explore their environment and experience things on a sensory level and a fantasy level. It's like writing. It's like software for their brain."