Depending of what do you want ?
A plan top? Horizontal, inclined ? A double curvated surface ? etc...
The more easy : draw first your curvated Surface
Draw 2 curves perpendicular, different or not ( arc circle, free form etc..) or take any surface you want : Make a simple Sweep
Then extrude from the ground object your base flower curve
Boolean Merge the sweeped curve and the extruded surface, Keep that interesting you, Boolean Union Cap and lateral surfaces, Fillet
that's All :) 10 second in a rusted state! :)
Of course your start surface can be any complex you want or even a simple plane!
Close directly your proposed curve is some difficult!
In some case Rail Revolve, Nsided can do the job but alas not here (too circonvolutionated)

|