Jumps :
If you can, build a moto/bmx style jump line. The jumps dont have to be huge (10ft to 25ft) but in a line one after another. Maybe like 4 or 5 in a row?
Step overs and table tops because they are mellow and are great for learning new tricks.
Step overs are my personal favorite because of how little impact you get when you land.
Step downs are gnarly and, in my opinion, cause way more injuries because you cant really see where your going to end up until takeoff, and then you just drop out of the sky. Plus, gapers on the knuckle equal death all around.
Rails:
Do not make rails shorter than 12ft, thats just a waste of materials
Up rail on the lip of a jump (25 to 45ft gap) to landing
A long (20ft +) single barrel urban style down
6in Flat bar rails of any kind
Tubes (Like the milly tubes at brighton) greasy and perfect
Flat Down or Large Rainbow Box
Rail to tranny landing (like a dancefloor after a rail or jersey barrier)
Although, I hate those boxes with two large tubes on top on either edge. Stupid double grinds