@David Soest Just to clarify, those that are disabled, are not strictly limited to people in wheelchairs. 

If he later says he needs handrails, grab bars, wheelchair ramp, etc., then you should make those accommodations or allow him to make them at his cost.

I have a sibling with a disability & have been having trouble finding suitable rental properties that are wheelchair accessible that also accept housing vouchers.

I am curious to know if anyone has purchased a house that is already wheelchair assessable and kept the layout.

This includes how you are allowed to market the units, like saying "Second-story unit" instead of "No wheelchairs".

Suite feature oversized bathrooms including a jetted tub and walk-in rain showe with grab bars.The sleeping area features a King Size bed Outlets/switches/thermostat at wheelchair reach, FA strobe/horn devices, Wheelchair accessible door peepholesA pullout sleeper sofa in the living room ensures that this suite can comfortably accommodate up to four guests.

The steps are so steep that you could not possibly install a wheelchair ramp. 

Also considering putting in a wheelchair verticle lift to make it accessible.

Elderly authorized resident (not on the lease, tenant's mother) became disabled and needed a wheelchair ramp to get in and out of the house.

My initial anecdotal research indicates that there is a need for accessible units that include wheelchair accessible restrooms, kitchen and ingress/egress.