
SD No. 0254/2012 [Taken from the IoM Government website 2019-10-05]
"Town and CountryPlanning (Permitted Development) Order 2012
SCHEDULE 1PART 2 —OPERATIONS WITHIN THE CURTILAGE OF A DWELLINGHOUSESection A —
General Conditions (1) No part of the development may be constructed within 9 metres (measured at ground level) of the route of any overhead electrical line carrying 11kv or more (High Tension power cable);
(2) No part of the development may be constructed within 9.1 metres of the bank of any river designated as a Main River under the Land Drainage Acts;(3)The construction (including foundations) must not involve the felling, lopping or limbing of any tree (other than a tree referred to in section 3(3) of the Tree Preservation Act 199315) or interfere with the root system of any such tree.
Class 15 Garden sheds and summer-housesThe erection of one or more garden sheds or summer-houseswithin the curtilage of a dwellinghouse. Conditions: (a) the general conditions applicable to Section A; (b) the height of the garden shed or summer-house must not exceed 2.8 metres above ground level; (c) the area of ground covered by the garden shedor summer-house must not cumulatively exceed 15 square metres in total; and (d) no part of the garden shed or summer-house maybe nearer to any highway which bounds the curtilage of the dwellinghouse than —(i) that part of the dwellinghouse nearest to that highway, or (ii) 20 metres, whichever is the nearer."
If you need the full chapter and verse, here is the link:
Isle_of_Man_Town_and_Country_Planning_(Permitted_Development)_Order_2012Saves expensive demolition costs and you can see why doors are often only 6' tall in these structures, so that they can comply with the overall maximum height of 2.4m (8')!
In my circumstances, I was replacing an old garage + two additional greenhouse structures with a single workshop on the same footprint, so didn't have to obtain planning permission, provided I didn't exceed the overall height of the previous garage, or finish the workshop in sky, blue with candy apple pink elephants!

Sorry that I cannot offer a building service. As for digging up useless or otherwise information, it was all part of the job when dealing with Land Tribunal cases in the forestry industry. Is the claim being made in the proposed 'work plan' actually practicable on the area of land for which it is proposed? Some people pay 'Consultants' a LOT of money for a bit of paper that you wouldn't use to wipe your ****!

Thank you for your compliments.
Good health, Bill