How to identify source of water coming into house?

[con_66]

Recently repainted bedroom and added new built ins. When old carpet lifted to relay new carpet there were two damp patches on yellow tongue flooring. Plumber has indicted sub floor - no water leaks. Builder indicted bricks/windows/roof - no water entry points. Two different areas of room. Have used dehumidifier/drying. Surface dries then hours later wet again. Subfloor area dry. House on piers. Any suggestions of what to do? Desperate!!!! 

[con_66]

Hi Eric. Thank you for all the info. 
Flooring that is damp is yellow tongue flooring in two different areas of room. Plumber, building/pest inspector have examined boards underneath damp patch (underside of boards dry except gif a very small area). No moisture detected in any other floor areas, walls, ceiling or roof cavity. House on bearers and joists. No water damage or moisture in sub floor area.