step 1-get out the base plate
step 2-insulate one end of the track
step 3-insulate the end of the 4 track pieces
step 4-add supports. the large stack has two 1x8s and the small one has a 2x4.
step 5-add another layer of bricks; this time put 2X4s instead of 2x8s
step 6-add supports. the large stack has two 1x8s and the small one has a 2x4.
step 7-add a light in the small column. see diagrams 


|-|-|
|l|-|
|l|-|
|-|-|
diagram of this layer of the small stack. 
|-|=stud of a 1x2 brick 
|l|=stud of the light


|b|b|b|b|b|b|b|b|
|l|l|l|l|-|-|-|-|
|l|l|l|l|-|-|-|-|
|b|b|b|b|b|b|b|b|
diagram of this layer of the large stack. 
|l|=stud of the light sensor. 
|-|=nothing added.
|b|=stud of 1x8 brick

step 8-add part of the wire to the top of the light. put two 1x2 brick next
to it, and put 1x8 plates
step 9-put a 2x2 plate over the wire. also, put a 4x8 
plate over the large stack.
step 10-add a 2x4 plate over the small stack
step 11-add the rcx.
step 12-wire the rcx. 
port 1: light sensor
port a: lock on clip attached to insulated section of track, attach its wire end to port a.
port b: light

downloading the program:
the mtss.vi is for robolab (tested).
the block.prg is for rcx code 1.0 (untested!)