Building a 30x30 building

I want make a 30x30 sky platform. Even though I have the centers of the outer walls at less than 30m it still won't link.. I can move the walls in to 20m centers and it will link... but then I an go into "Edit Linked parts and move them back out to the edge of the skybox floor, they jump back the postion they where in when I linked them... I own a 30x30 sky box so I know this can be done.... What is the trick? Can anyone help me?

Try making the walls from large hollow cut prims instead of large thin ones. That is, assuming you wanted a wall section 10 meters high, 10 meters wide, and 0.5 meters thick, start with a 10x10x10 cube and hollow it to 90% or 95%, then cut it with path start and end values until all you have left is a flat side with beveled edges. That way SL sees the center of the prim as still being the center of the original cube, quite a ways in from the edge of your platform.

You can also make corners out of a single prim this way by only cutting part way.

The trick is simple. Stop trying to make it a single linkset. There's absolutely no advantage to doing so.

You can make a flat 30x30 platform and link it, because the centers of those prims are all within 32 M of each other. Not so a pair of wall prims on diagonally opposite corners. You could use cut and hollowed prims, as another poster suggested. Or just use normal wall prims and link them up into multiple sets.

Ahhh thank you soo much.. Great ideas!
I just want it to be one link set so I can move it around easier.. I had not thought about the cut out... I can see I have a lot of learn about building... Thanks again!

If you manage to "just" link something like that, it will explode into pieces when rotated. Maybe not today, or tomorrow, but it will- randomly, and terminally. It's not worth the risk to build out to 30x30 bases in a single linkset IMO.