The recycling shop was looking to offload the Lego at $30 a kilo between 6pm - 9pm to help raise money for the Canberra Hospital Foundation.

Green Shed co-founder Elaine Stanford said keen shoppers had lined up an hour early despite the oppressive 38-degree heat.

"We brought them into the shed to keep them out of the heat," Ms Stanford said.

"It's great. Everyone's hyped up and all the owners are here and we're just giving mini-figures to the kids for free. We've just got cold drinks in the fridge and we're keeping everyone entertained."

One person had shown up as early as 7.30am from Orange in New South Wales, but left because it was too hot.

Ms Stanford said the ACT Rural Fire Service had offered to help with crowd management, but she had already organised extra security and staff for the night.

The ACT government even chipped in, helping manage traffic and notifying road users of a "special event".

"We've got rules in place, we've got security here and we've just handed out pamphlets saying be nice because it's going to a good cause, so there's enough for everyone," Ms Stanford said.

Each person was getting two bags, which could each hold a kilo, but Ms Stanford said that could change depending how it went.

The money was going towards a new MRI trolley and the refurbishment of the parent's room at the Canberra Hospital.

"We love stuff like this. We've been preparing all day in the hot shed," Ms Stanford said.

The Green Shed had slowly been accumulating Lego before Saturday's sale.

"We wanted to get rid of it and thought it was for a good cause," Ms Stanford said.