It will depend on several factors, your credit being chief among them. 20% may be possible, but 25% may be more common. Buying investment property can be a great way to gain wealth, but you must qualify for the home without it being rented first. Most lenders will not anticipate your income, but would use it for a refinance once you have an established history of receiving it.
Your first step will be to meet with a great lender experienced with this to find out if you qualify and under what terms.
If you need a local referral feel free to contact me. I have some great lending sources, having been a licensed lender for many years.