FORT WORTH (CBSDFW.COM) – A major construction project is underway at Cook Children’s Medical Center in Fort Worth, but for this build, some of the patients are helping out.

Thomas Park, 13, has always loved building things. “Ever since he was 2 years old he wanted to be a builder or an architect,” said his dad, Doug Park.

“Anything that involved building was a passion for him,” his mother, Beth Park, added. “This is a big dream come true for him.”

Thomas is currently working on his biggest project yet. He’s helping build a scale model of the hospital made entirely of LEGO pieces.

“It’s about 13 feet by 9 feet believe it or not,” said Dan Steininger, a Master Builder for LEGO. “It’s enormous!”

“Well, I’ve always liked building with LEGOs,” Thomas said, “When we came to the hospital I kept seeing different parts of it that looked exactly like LEGO pieces, so I thought it would be really neat if we could build a model.”

He came up with the idea five years ago, when he was a patient at the children’s hospital.

“I had cancer,” he said. “Rhabdomyosaroma.”

Rhabdomyosaroma is a tumor on the muscles that attach to the bone.

Doctors discovered a cancerous tumor near Thomas’ pelvic bone when he was just 8 years old. He was immediately admitted into Cook Children’s Medical Center where he underwent surgery, and chemotherapy.

“We were suddenly thrust into a situation that was scary and unexpected,” his mother explained, “and having the LEGOs to build with was comforting for him.”

“When you’re under cancer treatment you feel terrible, there’s nothing you can do, you can’t go out and play, you can’t do anything,” his father said, “so LEGOs is the perfect thing to do while you’re in bed.”

Now in remission from his cancer, Thomas is working alongside LEGO Master Builders.

“I actually get paid to play with LEGO,” Steininger said, “Anytime we get to hang out with kids is great, and then in a hospital setting, like this where we’re able to build a scale model to the hospital it puts it over the top.”

The model contains more than 800,000 LEGO pieces.

It’s expected to be finished Wednesday and will be on permanent display at Cook Children’s, which is only the second hospital in the nation to have a LEGO replica.