Im wanting to build a shed for my tractor and was wanting to know what the cons of a gravel vs concrete floor would be? It will be a three sided machine shed type building.

hands down concrete if it's in your budget can always pour it later.

Gravel =, Dust, rust, rodents., cement, non of the above.

Concrete is nice if you're wrenching and need to lay down. If you drop a small bolt or screw on Concrete you may actually have a chance at finding it. Only real con to Concrete is the cost, is it worth it to you? Personally my storage shed is gravel, at this point ide rather leave it gravel and take a trip to Hawaii because that's how much it would cost to pour it.

In my pole barn I have concrete,back in 2014 it cost me 5k for a 30x40.

I have 1.5 hours on my new tractor so I'm a subject matter expert.
I think dropping attachments is the only concrete issue to overcome. I have concrete in both buildings that my tractor will be stored in- I have a high ceiling in one that has pallet racking, I plan to rack attachments once I get a set of pallet forks. I made some roller-skates for the tiller and brush hog- it's already worked out really well for shoving stuff around when I'm in the shop on the concrete floor, allows you to push implements against the wall and roll them up to the 3pt.

Our tractor shed has a dirt floor. We do have a concrete floor where we fix equipment.

Our big barn is dirt floor for putting equipment and such under cover, out of the elements
Barn has a separate shop section that is concrete. This is for working on equipment

All my attachments stay out side.

Cement it’s clean, dry you can work with a creeper on it to work on things for maintenance, unless it a pole barn park it until you need it thing I’d stick with concrete. If you have bigger plans for the future consider running floor heat lines when you pour the slab, just a thought I wish I would have done that in my fur shed.

Shed has got a gravel floor. If I need to work on anything, large sheet, corrugated cardboard goes down, more for me and my back. Concrete would be great; but it's expensive and for me, I known it would be a pain to keep it clean.