Yes a down payment on your home is deductible...but probably will not "actually" be deductible because of the 3 part test.
See more on that 3 part test on the Housing Allowance page by going to the top of this site...click Topics...then "Minister Taxes"...then go down to click on the Housing Allowance link.
Usually the fair rental value of the home, plus actual costs of utilities...limits the ability to use that large expense.