Legal advice on leasehold deeds

Hi,

I am considering purchasing a leasehold flat and would like to know if the property deeds would allow the Freeholder to prevent me from converting the loft space into habitable rooms. Said loft conversion would include removal of the existing roof tiles, battens and rafters.

Further, do the deeds suggest anywhere that the freeholder can charge me a fee for granting me consent to carry out the building works?

More generally, do property deeds (not just these ones but all property deeds) make it clear whether a freeholder can charge for the consent? I'm aware the freeholder can often charge 50% of the perceived uplift in property value if the works are completed.

Thanks!