what options are available for building own patio without being able to dig required depth due to roots?

In a battle between three roots and patio paver stones, the roots win every time. The only two options I see are an on-grade deck or pea gravel area instead of paver stones. They are each not without downsides and if this is an addition to an existing patio, a low deck may look awkward. But an area of pea gravel 6" deep or just about can be designed around  the existing patio and become a nice transition to grass. Pea gravel is not maintenance-free, needs to be periodically raked and weed killer sprayed but it looks nice and natural and is permeable in case your municipality has limitations on the amount of impermeable surfaces on a property.