I'm coming up with a monthly gardener expense of $30 and a (TBD) expense for snow removal.

How is up to you , but a garden sprayer with a soap and water mix sprayed on the tiles stops any dust .

We take care of the shrubs/trees for all of our properties, but the garden beds and lawn care are sometimes done by us and sometimes done by the tenant, depending on what we write into the rental agreement.

I was thinking to use cash to build separate structures on the property (garden studio/guest houses?)

One could have reduced rent for a unit so a tenant would mow the lawn, another might pay $100/month for a gardener.

They specify that roofs, roofing tiles, slates, windows, floors, ceilings, walls, stairs, doors, skirting boards, fascias, tiles on any floor, ceiling and wall, gutters, down pipes, fittings, furnishings, gardens and common areas must be maintained in good condition and repair.

Lots of families and roommates don't need to live in the same unit all the time but still want to "live together" and pool resources.I live in a 2BDR/1BA in Santa Barbara with a small 1 room studio (no bath) in the garden.  

I am currently working on a land acquisition in Upstate New York that I will be installing a small/medium 'solar garden', but I am also exploring options for a small LEED housing development to go along with it.

They wanted be to put a door in and turn it into a roof garden area!

But, if you think it will be a good appreciating asset and you buy it with the intent to hold it and do something productive with it like share crop it, hay it, put it into a govt CRP program, lease it to hunters, put a "Pick your produce" garden market on it, grow cows goats or alpacas on it etc etc and then decide at a later date that it has probably met your long term return on asset criteria and sell it at a nice profit and 1031 then you are demonstrating your intent to hold it for productive use.