the accurate way to price the land is like this (as an example):
Total Land Area: 1000 square feet
Footprint: 50% (500 square feet built on, 500 square feet left as grass)
Floor to Area Ratio: 1.0
Maximum Buildable Area: 1000 square feet (500 square foot per floor)
Construction cost per square foot: £150
Total Construction Cost: £150,000
Sale Price of House: £300,000
Developer Profit: 15% (£45,000)
Land Value: £105,000
Take that £105,000 and divide it by the area and you have the estimated price per square foot. Multiply it by what you're selling and you have the price you should theoretically be asking for it.
Replace all the numbers you want as it relates to your property
bear in mind you're selling an unbuildable portion so you should in theory apply a discount or price it as agricultural land
I think I managed to follow all of that but out of curiosity how does one determine the floor to area ratio? is this set by the council or land planning authorities?