Here's a possible solution.
1) Place the standard 'Skylight Dome Circular' object onto your plan. Set most of the parameters correctly. This original GDL object does not allow you to set different X & Y parameters.
2) Select & then save it as a new GDL object.
This new object will allow you to set X & Y parameters unlike the original, which you can then set as an oval.
Unfortunately you seem to loose all other parameters which the original object had such as slope. This can be addressed by adding rotX & rotY in the GDL Script.
Haneef Tayob
Aziz Tayob Architects
AC23 INT rel 3003, OS X 10.14.6 iMac 3.3ghz i5 dual monitor, 24GB RAM