They are subbing by far the worst part of any builders clean.
This is also way more complex than you can imagine, not the clean, but the relationship between builder, cleaner and window cleaner. Off the top of my head I can think of CSCS, Liability Insurances, Risk Assessments, H & S Certification, Liability for Damages (which is a minefield and often includes a thorough documented pre-inspection that must be completed prior to touching the windows, when it is actually impossible).
The builder will also have to authorise sub-contracting, this is usually frowned upon. 3 years may turn into 3 hours if this isn't above board.
All of the above means nowt if they are offering full time employment and all the associated benefits and responsibilities, although I doubt this very much.
Looks like they've took on more than they can cope with and are now looking at ways of covering there butts.
We recently lost out on a big site in Longbridge to a much lower quote (AKA undercut

). At our rates I'd struggle to offer a good deal subbing windows, if this turns out to be the site we bid for then I'd love to see what's on offer.
Anyone finds out then post and I'll tell you how feasible.