I was just about to respond about the window entry problem of blocking the other residents windows too!
Generally, adding a passenger lift, even a small one, to the outside of a traditional tenement building will be hugely problematic for many reasons:
1. Is your tenement a listed building?
2. Is it in a conservation area?
3. Is it joint ownership ie you own your flat, your neighbur owns theirs, some HA owns another etc and you all pay for common repairs and maintenance?
4. Is the existing close arrangement: front door, long corridor to rear, stair up to half landing, 180° turn, stair up to 1st floor, 2/3 flats off landing then up to next floor etc, with each flight right next to the other?
there will likely be no part of your flat that is not directly above the flats below ie you cant have an area on the ground floor, within the tenement, that is clear all the way up to your flat.
To take a lift from ground up to your flat only from the front would foul the pavement, which you do not own, or the garden, which is presumably common ownership or the ground floor flat ownership. It would also require planning permission, which would be a tough one even not counting point 1 and 2 above. Even without all that, as mentioned, the shaft would foul everyone elses windows all the way up.
Taking a shaft up the rear
would lessen potential problems with planning, but again you run in to the window issue on floors g, 1 and 2 before getting to yours. You would also still have to get to this - are their stairs down from the close to the back court? And again, the back court will be common ownership and some have it written in their deeds that they are for clothes drying only and nothing to be built there...
So that doesnt leave much room for manoeuvre im afraid. Even if you were to solve all these problems, when you factor in the costs of ground works for the lift pit, shaft wall construction, works to tie in with existing fabric at all levels (especially yours), purchase of lift, maintenance of lift, construction of new roof over lift (depending in where in loft it comes out), plust the professional fees required - architect, engineer, lawyer etc, and then the timescales on something so out of the ordinary as this, then it would seem to not fly, sadly.
I had considered how the accomodation of lifts could be made generally in Glasgow tenements when I was visiting a really poorly maintained close on the southside recently. The back of the tenement was coming away from the rest of it due to apparent water issues under the buiding. There was a gap between the half landings and the back walls you could fit a dead dog in. Anyway - remedial work would need to be carried out to brace the upper floors along with ground works etc. At this point, you could prop the existing stair well walls, take out the existing stair and put in an entirely new stair and lift 'pod' either partially within the space of the existing, or to the rear in the back court. Cost could be partially offset by using the space in the stair well to extend the size of the flats (which would require altering internally, again adding cost)
So no quick fixes at least from the glance I have had at the issue, which is a shame, as the problem will only get worse with an ageing population and a recession meaning people with no ability to move out of their own homes to easier accomodation. So it is one good thing about modern regulations that ask you to take in to account the whole life of a building and its owner so lifts in common areas, rooms that can be amended to include showers, space in stairs internally for a stair lift to be fitted etc.
Perhaps a stair lift int he close would be the most realistic option?