making a gate tower

First  of all make a cylinder, and on the parameters set it so that the height and cap segments are set to 1 and the sides are set to 18.
and then just create a large Cylinder.

 Rotate this cylinder so tat it is up-right at 90%, and then on the measurements set the height to 180. Select your cylinder and on the modifier tab select slice - set this to 180

 goon polygon mode and then select the bottom polygons of the shape, and then extrude this by 128

 Inset the tombstone shape by 8, then extrude by -4, do this a couple times to create a 'stepped edge' – do this as many times as you want.
Once done, delete both sides of the inside polygons.

 Go onto edge , select the two inner edges and then select bridge – then go onto polygon and select the newly made poly going around (due to bridge) and then extrude this by -8 (ensuring that the drop down on the extrude menu is set to local normal). This will create an inset.

 After that, you then select the top polygons, delete them. Then go onto edge tool and select the top rectangles and drag them up, with the top still select bridge the top. Then select border, select the front border and ‘cap’ it and the back

 we then made a plane (easy to see in y frame mode by pressing F3) and made sure it was just big enough to cover the hole. From here with the plane selected you go onto the modifier list and select ‘lattice’  this will give it a gate effect. You then scale your gate tower so that it can hide the lattice properly.

You can then add detail as you see fit.