should i place a plastic on the ceiling?
When i had taken of the drywall from the ceiling in the shower, i did not find a plastic. It is my intention to place tiles in the ceiling of the shower.
This shower is in the first floor. As well, i did not find plastic in the walls. Except on the "outside wall". i found insulation and plastic sheet.
I am planning not to remove the bathtube..the question that i have is:
1..should i place plastic sheet all around the shower?
2. how far from the edge should placed the cement board?..1/4 inch??so avoid wikking?

You don't need to put plastic on the shower ceiling. There won't be a significant amount of water to reach the ceiling, and what does get up there will evaporate, run down the walls, or drip on the floor. However, a cement board of some sort is advisable on the ceiling.

1. If you are installing CBU around the tub with no waterproofing on the CBU, then yes, you will need a vapor barrier behind the CBU. If you plan to waterproof the CBU, then no vapor barrier is needed.

2. 1/4" is fine. Fill the gap with silicone.

1/4 inch above the base of of bath tube or 1/4 inch above the edge of bathtube?..this bathtube has a 1/2 inch of "border..PLEASE clarify..i am a little confussed...about the 1/4 inch..THANKS FOR THE REPLY

The cbu should overlap the tub lip, and be 1/4" above the tub deck.