Good Question. Below we have tried to indicate possible costs - this isn't a sales piece, more information. - If you'd like to see our kits go here. Otherwise this is an information post.
There are quite a lot of variables, such as post code - The market dynamics mean a roof in London and the SE will cost more to install than a roof in say Leeds. This is due to labour and overheads costs being higher.
The big question however is are you going to do this yourself or pay for a builder/roofer to do it?
The cost impact for DIY is highly beneficial on your bank balance. Modern rubber roofing kits, such as those supplied by RKD and others, are very easy to install if your are a reasonably competent diyer (especially if you can get a mate to help). There is lots of advice and installation guides around, (RKD supply this) - it's not rocket science.
Obviously cost is dependent upon roof size , overboarding, new woodwork and so forth - so to give you something to work from we will use a 20sqm roof (typical garage or extension size) as an example.
A reputable and professional installer will charge about £85 per square metre for install - this would include OSB3 overboarding of the current deck once stripped back, all the materials and edge trims to complete the job in total. So the professional builder will charge anything between £1500 - 1800 for the 20sqm roof - probably more in the SE/London.
You also need to consider access, height, is scaffolding required etc which will increase the bill (not considered below).
So what do the materials cost?
Well a 20sqm EPDM flat roof kit from RKD will cost about £330 - Trims, materials and tools included. Include delivery and VAT this would be an overall cost of about £425 for a life expectancy of over 30 years.
What about the woodwork - well RKD recommend use of OSB3 T&G boards which cost about £20 each (we don't stock these) - you would need 14 or 15 for a 20sqm roof - so with delivery let's say £300
Therefore the total cost of a top of the range rubber EPDM roof kit materials - including boards would be around £725 - All you then need to decide is if you are going to do this yourself or get a roofer to do it.
If you choose to do it yourself and have a mate to assist you can do this in a full good dry day. If your roof is complex with upstands and penetrations allow a little longer.
So if you have the time, do it yourself - If you don't, and many don't, make sure you get at least 3 quotes, and if you can, get a personally recommended roofer who specialises in EPDM installation.