Thinking of building a non-combustable material shed

[functor]

Hello all,

This is regarding a 30sqm "Garden Office", including insulation and electrics, heating

The roof will be lean-to and is capped at 2.5m due to it being near the border.

Due to building regulation issues regarding wooden sheds near borders, would it be cheaper to:

1) Build a brick shed
2) Build a metal shed
3) Build a PVC shed (is this non combustable?)
4) Get building regulations for a wooden shed near the border (fence)