Air Conditioning - Reinstalling A/C package on roof - should I?

I am doing a major addition to my house (basically it is all new). Floors, walls & ceilings are insulated & well sealed. The finished house is 1670 sq.ft., with an average ceiling ht. of 8.5'. The system is a package unit (Arcoaire) with heating & cooling, 3.5 ton, and was running great when we pulled it off the roof. Actually it was very much oversized for the house before the addition. It is 6 years old. I would like to save a chunk of money until cash is more available in a few years. 1) Is it a good idea to reinstall it?

Second question - What is the best way to set it on the roof: 2a) Previously there was an open metal frame with the ducts visible from the outside before they penetrated the roof through duct flashing. I kept the frame, and the new roof has the same pitch, so I expect this to work but not look attractive.
or 2b) Build a box frame on the roof , weatherproof it with flashing, and a cricket to divert water, and use the duct openings on the underside of the unit to enter the attic. (the unit will be on TOP of the box, NOT INSIDE). The issue is, how to best weatherproof this? I wish to do it this way, but no roofing books detail weatherproofing HVAC installations.

most downflows have better airflow.
the brand of unit you have is not one of the top, but if it is working ---keep it.
the size is good and if you did a good job insulating the house, the unit will be fine.

there are jacks that support a downflow application, or have one custom built. You will need the model number of the unit, pitch, height to the spanish lock- 1 " bend out- if you have it. As far as building crickets, and diverting water etc.. just be creative and think logical and you will be fine.

Thanks, azAir.
I am insulating the house more efficiently than required code standards (L.A. city).
I am unfamiliar with the "Spanish Lock". Could you provide more information on this?

Might check and build a wood frame out of 2X To fit the pitch of the roof. That the unit fits down over it that 1 " that most units do. Step shingles on the side and a cricket at the top. Counter flash it all. Then set the unit on top of this.
The issue is, how to best weatherproof this?
With the ducts out the bottom of the unit and the unit overhangs the roof jack. Everything should be ok

most elbows that come off the side of the unit go to a jack. this jack has a lip that is approx. 3" off the roof and the flange from the elbow wraps around this " spanish lock" - the lock is about 1" and is around the entire jack.

It folds around this.

I hope this helps...