Formerly a derelict chapel, married couple Martin and Sue Stephenson bought the property for £27,000, and were living in Shrewsbury when they converted it into holiday lets.
They moved into the old vestry at the property in Abergynolwyn more than two years ago to enjoy the beautiful scenery.
The property comprises two luxury homes, with a total of seven en-suite bedrooms, fully furnished and with a sauna, hot tub and baby grand piano.
They have to sell 330,000 tickets, which will cover the value of the building, the promotion costs and a £100,000 donation to the Alzheimer’s Society.
The draw was due to take place in December, but the deadline for buying tickets has been extended to February.
Martin said: “We’d decided it was time to move back to Yorkshire, to be close to family and we’d seen other, successful prize draws.
"We saw it as an amazing opportunity for someone to change their life, whilst raising a large amount of money for charity.
"We specifically wanted to help Alzheimer’s Society as we’ve lost two relatives to the disease and three years ago my father was diagnosed with dementia”.
A property prize draw isn’t for the faint hearted and involves a lot of research, to ensure that everything is done properly and legally.
“Property prize draws do not require a licence and are not regulated by the Gambling Commission, but it’s very important to ensure that you’re not running an illegal lottery," Martin said.
"To do this you need to either include an element of skill, in which case it is a prize competition, or offer a free entry option, which makes it a free prize draw with paid entry route.
"Most of the successful prize draws have taken a ‘belt & braces’ approach and included both."
Martin and Sue were in a good position to manage their own promotion, as Sue has worked in marketing for many years and they have set up and run several successful businesses.
They did their own exhaustive research, took advice from lawyers and The Institute of Promotional Marketing and spent months studying other prize draws and the reasons for their success or failure.
Sue said that it’s not something they took on lightly.
“It has to be done properly, as you only get one chance at it and it involves a significant investment," she said.
"There are several costs involved and you need to be prepared to pay for a professional website and all of the associated fees.
"You need to know that if there’s a big spike in sales you have a database, server capacity and email capability to cope with the demand."
Sue said the couple have been constantly dealing with entries, marketing and enquiries, at all hours of the day and night.
"Social media is a wonderful vehicle for this kind of promotion but it requires attention 24/7, to manage it," she said.
"It’s a huge amount of work and can be quite stressful.
"Our biggest problem has been that when people see what we’re offering, many think that it’s simply too good to be true."
As with most house raffles, if the target number of ticket sales is not achieved, a significant cash prize will be awarded instead.
Chris Manley, Alzheimer’s Society philanthropy manger, said the charity was very grateful to the couple, calling it "an incredible gesture".
Tickets cost £3, or four for £10, and can be bought at winadreamproperty.co.uk
So far more than 100,000 tickets have been sold and the couple say they are confident of reaching their target in time for the closing date on Valentine’s Day.
The draw will take place on March 1.