neat, farm looks funny where is it from ?
would you be interested in editing together an airfield for them, maybe this one could serve as an inspiration:
http://www.hiveworkshop.com/forums/models-530/goblin-airfield-49372/?prev=search%3Dairfield%26d%3Dlist%26r%3D20
Dont get me wrong im not trying to convince you or something, just felt the need to since your edits are of an acceptable quality and we generally lack airfield, helipad, zeppelin hangar type models.
For the machine shop perhaps the Dwarffactory.mdx in this:
http://www.hiveworkshop.com/forums/requests-341/3-different-model-edit-their-icons-request-258531/
can serve as an base for conversion given its long shape.
SoC Resource Pack has an neato Goblin Doppeldecker if you require something equivelant to Dwarven Gyrocopters. There is also an bomber plane on wc3c.net potentially to be used as an air unit, beside of the War zeppelin on this site, incase you are looking for some.
For the Goblin Merchant building you can try to convert it into an Manufactory/Smeltery, it would be like scaffolds and silos(or fuel tanks) over an giant furnace(or tank) in the middle where its now staying in the air, with a couple robotic arms that take chunks of molten metal from the open hatch smeltery and smith the item on the spot or pass it down an crazy goblin-tech gadget(Anything-a-tron 9000) that produces the desired item on the spot.
*Just an comedic idea.
Given the odd shape of that building i always thought something was below it but then they decided to not have it and cut it out, could have been something like an giant alchemy oven or such.