Dryson your post history tells me that I need to start this way, you have two paths to follow.
The first is all to common with you and it is best illustrated in your responses to Do Little above. You do not like what he has to say so instead of taking his comments as constructive criticism and using that to look at your idea from another angle you choose to heap scorn, contempt on him instead. If you are going to follow this unfortunate but all to common path then my response is simply -1, terrible idea.
On the other hand if you are able to sit back and realize that comments made by others like Do Little and myself are not personal attacks against you. If you are able to see that we are simply pointing out what we believe to be problems inherent in your idea, problems that need to be addressed before the idea could work in game then I am willing to expend the effort to assist you.
One last comment and a request before I begin. This is your idea, in the current form as stated in your OP there is insufficient information to paint us a picture of what you really want, as a result it is your responsibility to change the idea, flesh it out as they say to the point where we can finally see what you really want. Now that request, please do not go back and edit / alter your initial post, doing so removes the context of responses such as mine here. Leave the initial post stand and use other posts along the way to restate your idea so all of us can follow the progress of change.
So with nomex and kevlar garments firmly in place here goes.
To be relevant capsuleer ideas need to be workable within the confines of the game AND it needs to provide both risks and rewards that are in balance to the effort expended and your idea as stated fails miserably at all of these.
Materials needs for the current citadels is for all practical purposes an impossible task for a single player. Given that what do you propose this new structure would require for materials, specifically what types of minerals and how much of each would it take?
How about capabilities of the completed structure? would it have the same functionality as a current citadel? if not what functions / capabilities would you suggest be removed or alternatively what capabilities should it have?
If these structures lasted until destroyed by other players how many thousands of them would we have hanging around in EvE? Given the current complaint level about citadel spam is this really a good idea to have even more of them hanging around?
If they only lasted a short while and then were automatically removed how long would you suggest they stay up? And given the effort that player invested in this “mission” if the resulting citadel automatically disappeared after a period of time what would that player receive in return for their efforts?
Does this new mission really need to involve mining, construction etc?
Why not simply refer them to the existing tutorials on these topics?
Perhaps an epic arc style is best here, we could simply take some of existing tutorial content and string them together to teach all the preliminary phases of the process. When they get to the final mission they would have something like a ship to keep for their efforts and in true mission form they would receive a structure they had to take out and anchor in space. Upon completion the structure disappears with the rest of the mission pocket in the end player has the experience you desire them to have and they have something they can keep that was a direct result of the efforts expended and we do not litter space with thousands of these new structures.