I have suggestion Richu
1.Generally underground works are mentioned under seperate WBS named underground works where we mention underground piping works especially for drainage and sewer works they does not come under first fix activities
2.Sleeves comes under a WBS called builders work they does not come under first fix activities ,even slab conduiting could be classified under this WBS but it has an option it can also be mentioned in first fix
3.Rest of yours is perfect
4.I would advise you open up WBS individually for electrical, mechanical and plumbing do not group as M&E fix or works for the ease of tracking ,cost and resource loading
5.Be specific in mentioning activities for example you wrote cold & hot water supply under 2nd fix ,please mention what work you going to carry out for example cold & hot water supply piping works
6.so that your programme is easily read by others without any communication problem
7.I guess it would helpful to you