Which is preferable in terms of getting the best result? 1. fixed cost maintenance 2. fixed labour costs 3. time and material

From a contractors point of view...

1.  If you choose this option, very likely you'll bleed money and make no profit. Not recommended unless your monthly fees are enormous, I've known clients to go around like kiddies in a sweetshop requesting all kinds of needless repairs.

2. Probably the best option but specify that you will only pay the first10% of the materials costs then it's up to the client to pay the rest. The emphasis is then put equally on both parties and if you do a good job you may end up with some small works near the end of the financial year when they want to spend up what's left of their budget to ensure they get the same or more next year.

3. Surprisingly, you may not make any steady money across the whole financial year with this option - the facilities budget is finite, once it's gone it's gone, and a client will often just put off repairs until the budget is renewed. It's better for the business to have a steady income month to month.

Note; A thorough asset condition inspection is well recommended first - if it's a new build then many of the assets will be under warranty for the first year and your parts costs will be low, you can charge a lower fee, on the other hand if it's a very old and hard used site then expect a great deal of repairs and budget accordingly.

I agree with Dean Waters