In this tutorial you will learn how to create an open umbrella quick and easy. It's not a detailed model, rather an easy to build object, ready to be deployed in larger scenes.
Start by creating in the Top View a sphere with a Radius of 100 units.
Go to the Modify panel and change the number of Segments to 18 and Hemisphere to 0.625. Convert the object to an Editable Poly (Right click > Convert To > Convert to Editable Poly) or throw an Edit Poly modifier.