Building offices/workshops to rent out

I did this about twenty four years ago with an old dairy farm for my then employer. Not sure if any of the current planning laws would apply from that time to today but I converted the loose-boxes (x6 off) into three units, milking parlour one unit, bull pen one unit & two of the covered yards plus the feed race into workshops & an office. They were filled with occupants witiin a couple of months and apart from enlarging the loose-box from three separate units into one nothing has changed. Before any interiour changes the roofs had been put into good order, new water pipes laid & a communal toilet block built.
I would say this is well into the 'profit' sector now. Rule one from the very first day was no motor trade. Several years later there was a motor trade occupant and lets just say 'never again'!
If you have good comms into the units and for offices you'll need to up the finish somewhat, you'll have happy tenants. Careful parking arrangements agreed in advance are important.
SS

Nah, conversion only.

Few farms are located where councils want new employment from scratch but they are happy to grant for conversion as a compromise

I would just put something up, get some peeps in and then apply retrospectively. Sounds rash but it does work, What are the neighbors like? Do you have any? Busy bodies in the local parish who may take an interest? we did it here many years ago. Some councils put some clauses in to stop change of use to light industrial from agg, but you can go for "storage" not too many vehicle movements etc and feel the water.
I believe you can do it all online these days (the change of use anyway)

Make sure there is demand for it before you start. Friend of mine converted a shed without checking and it stood empty for years.

Broadband, mobile coverage, access and parking are all essential.