"RTS" type "Wall placement"?

How to I make a 2D wall placement system? I am currently in the progress of an RTS game and I struggle finding a solution for this problem.

I want it to work pretty similar to the one in this video except less "Smoothly" It is gonna be a 32x grids.

I highly appreciate some help on this one! <img src="{SMILIES_PATH}/icon_e_smile.gif" alt=":)" title="Smile">

<img src="{SMILIES_PATH}/icon_e_wink.gif" alt=";)" title="Wink">

Edit1: Also i want it to be from this view perspective:

Are your walls only going to be horizontal or vertical; no diagonals?

Are your walls only going to be horizontal or vertical; no diagonals?

Yes, only horizontal or vertical. Not diagonals (Might put ut in if it is easier)

Well, it's not ideal, but this might help your on your way.

Edit 1: Among the problems it has-

Some weird behaviors based on the fact that while the cursor is at 15, 15 on a tile, your click-and-drag will be at an odd offset.

Nothing prevents walls from overlapping.

No special handling for walls intersecting

Not using different image for vertical vs horizontal walls once built.

Well, it's not ideal, but this might help your on your way.

Edit 1: Among the problems it has-

Some weird behaviors based on the fact that while the cursor is at 15, 15 on a tile, your click-and-drag will be at an odd offset.

Nothing prevents walls from overlapping.

No special handling for walls intersecting

Not using different image for vertical vs horizontal walls once built.

Thanks! I am going to look into this! Also i think i have som solutions for these problems. With the overlapping problem, isn't it possible to make the z order based on X & Y coordinate?