Importing Adobe Illustrator files as Parametric shapes in After Effects?
I don't think that it's possible to import AI shapes as parametric shapes (in 2019 at least, this might change, with luck). There are workarounds that can help though.

If you convert the AI layer to a shape layer you can get the individual points of the path like so:

var pts = thisComp.layer("test Outlines").content("Group 1").content("Path 1").path.points(t = time)


where the layer "test outlines" is the shape layer created by converting the AI document, and Group 1 is one of the paths in the shape layer. Then for a rectangle you can get the size like this:

var pts = thisComp.layer("test Outlines").content("Group 1").content("Path 1").path.points(t = time);
var size = pts[0] - pts[2];


if you want to set the size you could do the reverse, putting this on the path property:

var size = [123, 45];
var pts = [[0, 0] - size/2, [0 - size[0]/2, size[1]/2], size/2, [size[0]/2, 0 - size[1]/2];
createPath(points = pts, inTangents = [], outTangents = [], isClosed = true);


if you do the substitutions you'll see that the second line works out to

[-61.5, -22.5], [-61.5, 22.5], [61.5, 22.5], [61.5, -22.5]]


which describes a rectangle 123 wide and 45 high.