Various jobs - how much to sort (in London)?

[DannyG]

Hi guys - any help on pricing these would be most appreciated. I could perhaps DIY the simplest but mainly looking to employ others:

Provide water proof membrane to head of entrance porch (more a 0.5m2 shelter over step than porch actually)

Repair to 'flat' concrete roof (8.36 m2) and application of 2 coat mastic asphalt surfaces

Bricking up 2 external back doors which are sealed but not fully removed.

Replacing a soil vent pipe

Removing/sealing redundant vents in external wall

Thanks