This shape specifically, it's called an onion dome. I can't make it perfectly symmetrical using the curve tool.
Using the following method, you can edit the shape, or tweak the curves, and it will be automatically reflected on the other side.
Edit the curves, and the shape will be automatically reflected.
Starting with an uppercase S (Helvetica light) > Rotate it -30º
Add an ellipse at the top center of the inside area (green on the image)
Here's how I'd do it.... no guess work....
Object > Path > Add Anchor Pointsto add additional anchor points to the oval. -- Added anchors are always positioned exactly midway between existing anchors.
Convert Anchor Point Toolto move the Bezier handles of the top anchor down, Hold the Shift key down to ensure the handles are 90° vertical from their anchor. And move them both so the handle is in the same position under the anchor.
This animation is using AICS6, but it's the same steps in AICC.