animating irregular shaped masks

[stephenfinn]

this seems like it should be much easier than i am finding it.
what i want to be able to do is to be able to reveal the outline of a rectangle, from the top left corner, to the right top, to the right bottom, to the left bottom and up to the top left.
whenever i try to add a new element to the original masking layer it disregards it. i am tearing my hair out as this seems like it should be so simple.
any help would be very appreciated

[Tink]

try creating a mask for each side. then set of the first, when it reaches its target set of the second etc.

[stephenfinn]

the problem is that the two different object tweens wont go on one layer. im sure there must be a simpler way of doing this.

[Tink]

if your tweening it, i would have 4 layers for masks and 4 layers for the sides.