S1- Take Top plane and select it.
s2- click on sketch icon. and then select top plane.
s3- click on polygon option in sketch menu
s4- set no of side. for eg. take 6
s5- give the value of radius of polygon
s6- click on the position in the sketch where u want to draw in the selected plane
s7 click ok
s8- Extrude upto desired thickness