As far as I understand ( and I have applied this to enlarging office space) an IMB is required for a permanent structure only That is to say, something made from bricks, concrete, stone, mortar etc. A non permanent structure can be made from wood, straw, grass etc. when I had to extend the office of my previous employer ( G4S, on the Sanur Bypass, 300 metres north of KFC) we used converted shipping containers, professionally fitted out by a company in Surabaya.
The advantages are:
1. The building was classified as a non permanent structure, hence no IMB.
2. When the lease expires, you can take the building with you when you vacate the premises.
3. It was cheaper than wood, concrete, stone etc. ( about 140 million for 50sq m.)
4. It took 10 days from order to delivery
5. Low environmental impact ( Used Shipping containers)
6. Earthquake proof.
Its a bit like lego as there are infinite permutations!