This can be a potential problem. Firstly you should check that you do not own the area already. A qualified person will need to read your lease and advise on this.
Once you have established who owns the area, the position needs to be considered with your fellow participants. If you are the only person with access to this area, then provided the other people purchasing the freehold with you agree, it should be possible to obtain rights over this area and also permission from the freeholder so that you can develop this area.
Please bear in mind the following:
1. If the roof space does not already belong to you then you will need to buy it from the eventual purchaser of the freehold.
Sometimes this issue can be resolved by allocating the part of the purchase price relating to the roof area to you – in effect increasing your share of the freehold purchase cost.
If you go down this route you may need a specialist valuer or surveyor to provide an opinion on the price to be paid.
2. Owning the area means being granted a lease of the roof area. The company / nominee purchaser will have to agree to do this.
3. Under the terms of the lease the consent of the freeholder may still be required (and most likely will be) before any work can be carried out.
4. There may well be other applicable restrictions outside the lease or the title that must also be overcome before any work can commence. e.g. planning permission or building regulations consent. If the property is listed or in a conservation area further constraints may apply.
5. If it is your intention to do this after the freehold purchase completes it is as well to sound out the views of your likely co-directors in the freehold owning company in advance. If there is going to be disagreement then there is the potential for a ‘conflict of interest’ to arise and the same legal advisor may not be able to act for all of you.