How to build reef on sand??

I am setting up a 30 gallon reef tank. And plan to use a sand substrate and about 40 lbs of live rock. What is the best way to start the reef foundation?? Do I put the live sand down then build the reef on top or do I build the reef on the glass bottom, then add sand around it. Or finally, should I put in a plastic lighting eggcreate (is the eggcreat that you would use a ceiling light cover from home depot, or if not what is it and where do i get it??)then build the reef on that and then add sand? What is the best way to go about it??? Down the road I might want some things that dig... Thanks

 

There are pro's/cons to the two good ways above. I'm not versed in them though.

 

Here is a link to what I did with my tank. I am not saying this is the only or best way, but it really worked well for me. I am very happy with the set up so far.

http://www.3reef.com/forums/show-off-your-fish-tanks/my-new-120-gallon-thread-57116.html

 

You will definitely want to put the rocks dow first, then the sand. This is to keep the reef structure from collapsing if/when something decides to burrow in the sand, so they cant get under the rocks.
The eggcrate is up to you. Or you can use PVC pipe as well. Or you can just stack the rocks. If you use eggcrate/pvc you will have to affix the rocks to it though, which will make it harder to change the rockwork later down the road. Which is why I choose to just stack mine All just personal preference on that one though