The helicopter has a massive footprint which is in most cases impractical, the pad is even larger and looks terrible. With the use of moveobjects you can place the helicopter on the roof of you buildings easily and it will work without the need of the helipad. However if you want to roof your helicopter in and still have it fly, it's a little more tricky but still possible within a few constraints. There needs only be a single tile open in the roof of the building for the helicopter to still be used, I've identified it thus:
Once the helicopter has been placed though I noticed the lot had to play for a second before it could be used. This hole must be open on every level of the house in order to work, as such I can't find a way to roof over the Helicopter and have it fly when not using flat roofs.
I've tested placing the helicopter several ways on the lot and it appears to be consistent. But I initially thought the tile moved randomly so feedback might be useful.
Alas the blades to not harm people. Needs FIX!
When in use the helicopter does look very strange. It may be possible to link a custom animation vertical door though with the helicopter to open as soon as people enter it, but I lack the knowledge to do this.
Added:
It appears I've caused a mild bit of confusion. I've clarified myself with "without the need of the helipad" as I was already finding the pad ugly and was looking for an immediate way of removing it. Also I've removed the "by default can only be placed at ground level on a flat surface" as that was in reference to the basement helicopter design, if you want to have an underground helicopter pad it has to be done via the same method of an underground garage.