The former model - who received a £24.3 million divorce settlement from ex-husband Sir Paul McCartney last year - has appealed to plumbers, electricians and builders in the hope of getting the project underway.
She wrote on her twitter page: "Haiti is a mess at the moment can't believe we live in a world with such cruelty. I have two kids who's families were killed, they were burn't alive, had two legs amputated and managed to stay alive, no Parents.
"I'm trying to build a clinic for the orphans and amputees, any plumbers, electricians, builders fancy changing lives? (sic)"
The prospect of building an orphanage in Haiti is the latest in a string of projects for the 42-year-old star after her VBites vegan restaurant in Brighton, South England, shut its doors for a supposed "summer break" last month.
However, insiders recently revealed the eatery has been facing financial difficulties and is unlikely to reopen.
A source said: "I understand Heather has been haemorrhaging money on VBites for a while now. A six month 'holiday' isn't usual."