concrete slab up over vinyl siding
You can pour a new slab up to the level of the foundation, not higher. In this case,  you could basically fabricate a new concrete patio that's below the level of the previous one and build some steps leading down from the door to the patio.

You could also forget about making a concrete patio and build a wooden (or composite decking) patio at the current level of the door.

In general, I would recommend against pouring concrete right up against the foundation, because it provides hidden termite entry points and makes it very difficult for you or future owners to insulate the exterior of the foundation later (if this is an appropriate foundation insulation and hasn't already been done). Also, you have to get the slope away from the house perfect or else you're redirecting water into your foundation.