Me and my wife are planning to purchase her mom's house. 

We build houses; rehab houses; love our neighbors; and wouldn't think of living anywhere else. 

For a $100k house, we can agree on payment terms and pay the seller $120k over time.

Yes, the spring/summer season sees demand ramp up, but that doesn't mean a house listed in December won't sell.If you buy in October/November, chances are you won't be listing until January, anyways.If I had a house completed on, say, December 15th, I would likely sit on it through the holiday season before taking it to market, but I would talk to realtors.  

On one lot, he has his house.

Adding ADUs and renovating the existing units.

Also i suspect there is not as much offered here over existing options as some believe.  

Nick,Why can't you buy the house as a "rental" and then when you are not able to rent it out easily and then you can move into the main house and rent out the ADU. 

Calgary is going through a bit of a boom right now with house prices 10% higher than they were last year, everyones trying to flock from Toronto or Vancouver and find value there.

Hi, I got around 19k seller's credit for a house of 775k.