Bathtub install floor height

I'm renovating an upstairs bathroom and have stripped out the builder grade 60x30 steel tub and removed the alcove tiled area down to the studs. The tub was sitting on 5/8 ply subfloor and the finished floor is 3/8 sanded ply underlay and sheet vinyl butted up against the tub skirt.

My plan for the floor is to remove the sheet vinyl, install ditra and 3/8 porcelain floor tile. I'm still in the planning/purchasing materials process.

This might sound like a dumb question, (I was told there are no dumb questions only dumb answers) but to establish my flooring and plumbing elevations, would you install the tub on the 5/8 subfloor then tile up to the side of the skirt or have the floor finished then install the tub on top of the tile? What are the advantages/disadvantages of each install sequence?

Thanks for your help!
Dan
Go Canucks

No reason to install the tub on tile (unless you happen to choose an old-look claw foot tub!). You might stick another layer of ply underneath for strength and to keep the skirt from being burried too far though.

Tubs are usually installed long before the tile is put in. If the tile butts against the tub's skirt, then, if the grout/caulk seam fails there is a path for water to get through the floor, which is not the case if the tub is sitting on the tile. It is also easier to tile if you do not have to fit the tile to the tub.