I'm such a beginner too so just try gta forums coding section. Mostly Id like to start basic course and stunts can be added.
If you have ideas you can post a simple video of the run and edit in the checkpoint locations.
Coords for he construction site...which then will be followed by the original pcj playground mission:
234.814, -223.532, 10.416
259.237, -232.773, 9.633
308.072, -249.447, 14.630
325.022, -265.295, 19.403
335.526, -235.417, 28.186
331.603, -274.423, 34.420
320.316, -250.188, 37.215
327.189, -227.304, 34.627
451.131, -292.278, 9.064