Help please....

I have never used this software and so I'm most likely way off base here but it looks to me as if your pivot point is front center instead of true center. Again I might not be looking at it correctly.

 

Your building is not set at 0,0,0 and your plug need to be at front middle - see my example. Also make sure your pivot point is correct. click the image to expand to full width.

 

Well, I fixed your model. Added some pictures for explanations.


There is a tutorial for correct placement, I added that too, check attachments.


You placed your L1 model incorrectly, this is how it should be:



And here correctly placed layout helper dummies:



Link to fixed .max file:
http://www72.zippyshare.com/v/Vbj43vcm/file.html

Don't forget to export new layout file.

If you have more questions, feel free to ask here.

 

Yes you can change that:

Red markings: probabilty/chance of tree appearance (100 means always appear, 50 means there is 50/50 chance for tree to appear in that layout.)

Green markings: The size of the tree. It's the percentage of the true tree size, play with this settings and you will get size you want.

Yellow markings: Random scale, it's how random scaled trees appear in your lot. IDK if it has any relation to green marked scale.