Firstly as you indicate, it's not quite in the range of the average diy job It's mostly in the broad traditional sphere of carpentry/joiner, though fitters may just be specialists in erecting a manufacturers products
If fitted by trades people, there wont be any instructions.
You would need to decide on what you were looking for and if buying used, whether what you were buying fit into the space you have available, it would present additional problems cutting something down to fit to size.
You would need a base if for nothing else but to walk on These units aren't heavy, so the base need not be the same as traditional building work.
The base would normally be of concrete with a waterproof membrane,possibly insulated, dug out of the existing earth, and raised above ground to avoid standing water.
Some conservatories have a brick wall for part of the structure, called a dwarf wall. If chosen these would require their own foundations/base and require a competent brickie.
Others are full length with no brickwork, and hence remove that requirement.
glazing
Some may be single glazed, or a double sealed unit or polycarbonate.
Sealed units if replaced would need to be specifically ordered to size, single glazed or polycarbonate you could buy off the shelf.
openable windows v single sheets
easiest is single sheet polycarbonate..basically a plastic instead of traditional glass, It's more flexible, less prone to break, better insulation, often fitted to roofs with no openings; obviously no openings means you dont usually have the traditional window frame which is openable.
The frame which may be aluminium with pvc, starts with a ground plate bolted to the base, on which the first wall section is fitted to it and the property wall.
The next is fixed to that one, and so on till the complete wall is formed.
On top of that runs a perimeter fixing section where the roof rafters go, and rest on the end on the wall plate fixed to the property
wall where they form a sloping run/roof.
Polycarbonate sheets just rest on the preformed grooves, and are quickly in place covered by supplied finishes.
You can get lots of roof variations and apex variants, which requre further effort to secure and waterproof.
Its essentially building in sections, fitting and fixing in place and requires less skill than say timber construction just a screwdriver and drill etc and a careful eye so that you keep level.
That said its far from an afternoons job,even excluding foundations and any brickwork Most are fitted by trade, rather than diy
If you can find one cheap enough bearing in mind transport costs, and deconstruction, you might consider it. You can as joe said check the base size if its still in situ. If you take it down yourself, it will give you some idea of how it goes up, though allow sufficient time to do this.
Most of any sealant, flashings, other waterproofing will need to be replaced, and are readily available.
Check for end caps, the finishing bits to cover the cut metal, are there, also dont be in a rush to take it down and twist any metalwork.
Some screws will have lost their head, or just wont remove so have a plan on dealing with them while still preserving the frame
Good luck
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