Entrepreneur

Mate it sounds like the entirety of the plan here is to quit your job and do something that has to do with an empty space. That's a shit plan. Don't follow that plan.

Carpentry

Cabinet shop, automotive, some kind of light manufacturing.

Bitcoin mining, 3d printing, all seem like bubbles. What are you 3d printing? If you have viable product, just injection mold it. Bitcoin, really? Airbnb? Nope. Good old fashioned stable businesses.

Build trailers. Build stuff, that you can put on skids, wrap and wholesale, then work on making more and more. Or fix cars for $150/hour. Or build high end cabinets with CNC equipment and human input that go into high end kitchens.

Insulate it so it is 100% dark and silent inside. Charge $100+ per hour as an isolation therapy room. [Let people (individuals) walk around in the dark and bump into things, lol.]

You can also do themes on this, so add in brown noise or lighting synced to hypnotic immersion, etc.

I might want to do a community ceramics business. People can rent monthly access to throwing wheels and space. Not sure where you live but where I am in San Francisco there are about 4 within walking distance from me. A bit of a trend

Not sure where you're located, or where the shed is, but i'd do something like boat, caravan, trailer under cover parking on a monthly basis.

2800 sqft is nothing for real deal Bitcoin mining and be prepared to spend way more than 100k for a mining fleet.

If you had the knowledge and means to set up a 3D printing shop for a under-served niche you could make bank, but I think your space is more so for someone who is already running something and wants to scale.

There's honestly endless opportunities given your circumstances and capital, just do something that you think you'll find interesting and enjoyable.

Me personally though, I would either start a VR arcade or make a porn set and see who answers the ads to audition ;)

Limousine / livery service - ran one all through my 20s and if done well is a lot of fun and cannot be classified as commercial if you don’t have customers stopping by, which you never will - just a place to park, clean and repair the cars

Avoid bachelor parties!!!! Bachelorette parties are amazingly fun!

Where is it located? Easy to get to via transit? Thinking artist studios with keyfob access rent out 10x10 studio space and just frame it up?

Start a mushroom farm. Specialty mushrooms like Oyster, Lions Mane, Shiitake, Reishi, Cordyceps, Turkey Tail…

Honestly I would get large Klipsch speakers like Klipsch horns and continue running my laptop based business but blast music on larger speakers. I would also slowly become shit box jay Leno.

You can consider a custom merchandise business!

With my existing business, I would 1000% use that as studio space for photography and film.

Make it into an office rental space. Rent by the hour.

I was just thinking about something like this after talking with my boss about the financials of our warehouse.

You could turn it into a distribution warehouse where all you'd need is to get shipping containers brought to your property then unload the container and wait for the distribution request at which point youd rent a little truck and deliver the goods. A 20 foot container brings in about $2800 AUD and is usually completely sold within 14 days because after that point the company gets charged storage fees.

I’d pack every square inch of it full of random shit my family has acquired over the last several decades that we cannot seem to throw away.

Escape rooms

laser tag arena

rage room

axe throwing

indoor putt putt

indoor ninja course - ropes etc

antiques buyer and reseller

maker space

I would start now. Call it “Santa’s Workshop”

See, most people don’t want to construct their kids’ “Santa” presents at their own house, and they need tools and time to build these toys to perfection. They will need to store and transport the completed toys. And, they will need waste disposal of the packaging materials. These parents may even need handyman help assembling toys. All of the above is available for a fee.

What was the precious use? It may be allowed to continue in the residential zone as a “grandfathered” or legal non-confirming, assuming the space wasn’t converted to a residential use with a building permit.

Talk to a planner

Start collecting antiques and junk, and do a side hustle having garage sales 3 -4 times a year. Also you can sell on Facebook marketplace and eBay. No need to rezone to commercial. That's what we do. And it's an all cash business. And if anyone asks about your inventory it's just your collection.

Things like 3d printing, bitcoin mining, use it as a warehouse to buy and sell things from alibaba, all cross my mind but I have no experience with anything like that. So, I'm hoping for some guidance from some smart folks. If you had 2800sqft and 100k to invest, what business would you start?

You need experience or someone who has experience. E.g. You need a bulletproof contract form if you want to rent it out or else the renter can blow up the whole house and you will be the responsible.

I dont know how strict are the rules there but e.g. in europe you cant do anything anywhere so if you want to work with food you need to prepare the place according to that if you want to work with chemicals you need specific type of floor to prevent leak etc. If you find what you would like check if you have rules like these before you start your business.

The most simple is to use it as a base or office like if you would start to flip things on amazon you have place to buy big bulks for cheap and sell them in small parts for profit. Or you can store something that is cheap in one season but can go really expensive in other season like AC.

You could invest 10k and make a small storage unit and rent out storage spaces and utilize the 90k in establising your online business, I'd recomment dropshipping instead of having your own inventory.

if you have a big open space and proper parking then start a specialty gym.

fitness trainers and martial arts teachers are always looking for spaces to use.

you can easily bring in $5k a month if you're charging personal trainers and other people.

Pickleball courts! Especially if you are in a cold weather area.

Here is a simple fall back plan: Rent the garage to someone who needs it. And create a fixed deposit on the 100k you have.

I am not saying you should follow it. But you can find out the returns on this risk free plan and then compare the risk and return potential of all other plans you come up with.

Now, don't pick any plan that is not substantially better this default.

"If I only had an original idea, I'd start my own business" is something I have heard over-and-over.

You don't need an original or unique idea. You need an idea that you will follow through on and do better than most others who are doing it.

OP, what are you doing now for a living? What other things have you done? What hobbies are interests do you already know about? Can you already identify some kind of business where you think "I could do that better?".

Grow weed

That's my dream garage. Machine shop.

I had a 2400 sq ft garage. I grew medical cannabis. It was quite lucrative.

Use all that space to grow some wheat so you can feed cows. I hear cows like wheat.