Open this in customizer, play with the sliders, fiddle with the sizes and make something beautiful!!
___________
New Features:
I have added the possibility to make the middle thinner than the bottom and top. Use a negative value for the curve to get a thinner middle.

I have added a cylindrical hole so you can make candle holders, rings, etcetera

____
Tips:
Openscad has some limitations that cause some failures in the stl files for some of these models. You can use the netfabb default repair to fix your stl. You can find a manual here: 3daddfab.com/blog/index.php?/archives/10-Automatically-Repair-STL-Files-in-2-Minutes-with-netfabb.html

There are sliders for the wall and bottom thickness for vases, bowls etc. but if you can control the print settings you get nicer results with a solid stl model.
Customizer settings:
-Bottom thickness: Bigger than your height
Slicer settings:
-infill settings: 0
-top layers : 0
-number of perimeters: 2 or more
-bottom thickness: 3 or more bottom layers.

If you do not use support you should be careful not to get to much overhang. Overhang happens faster with:
- a bottom diameter that is much smaller than the top diameter,
- big curves
- big grooves