New shed a hoist plans

[syco26]

I am about to have a shed put on my property. The shed will be roughly 9m wide with two roller doors and 12m deep. I am getting it higher than standard with the the wall height of 3.6. I am planning on getting a minimum of a two post hoist but ideally would like a two post and a four post later down the track.

I have a couple of questions I am hoping someone could answer that have been through this before.

Question 1- positioning of the hoists.
Was thinking to plan the shed to have the hoists next to each other as soon as you drive in the shed but think that may be a pain for getting cars into the rear of the shed.
If I have them in the rear of the shed it will cut down the area I can have for workspace and areas I can devide later, ie. Clean room for motor work or spray booth.
If I have one in front of the other it will be good keeping one one half of the shed free for deviding but will restrict what I can do if I have one partially completed car sitting on the front hoist for instance.
Any thoughts would be greatly appreciated.

Question 2- floor thickness.
I have read heaps and there is a great differing of opinions on it. Will 100mm be sufficient for the whole shed but make the strip for the hoists thicker? Should I go 150mm for the whole shed so I can place them anywhere? Or does the slab need to be thicker still?
Once again any feedback would be greatly appreciated.

Thanks