Pair your generators, and nest them, lock them up securely, and bury them. With decoys.
I'm bouncing a bit off of Amadaeus' answer, in truth, but there are a lot of ways to add complexity and make the whole much harder to negotiate.
Start with a huge hole about the size of your intended complex (should be a sphere twice the size of the building, half sunk into the ground).
Then, take several generators, creating nested force-fields. From room sized up to just over twice the building size, perhaps. Leave a bit of space between layers, at least enough to hold a couple generators.
Lock each generator securely, with layers - cases or cages with complex locks, solid layers (like poured concrete), open layers (rubble, braced scaffolding, spikes, etc), puzzle locks, and a couple fail-safes (anesthetic gas, or things to tangle or trap, setups to injure, etc).
Pair each generator with another generator (also locked in layers), set at the very smallest size, or else just enough larger to hold both generators and their assorted locks (depending on actual size of generators). Turn on the second fore-field and fill it with rubble, dirt, etc.
If it is possible to have variations in the generators, do so as much as possible - even if the mechanisms are the same, perhaps a varied physical layout is possible, different access panel locations, different wire organization or color coding, differently shaped casing for internal parts, different interfaces, anything that can make disabling a second generator different (or apparently different) than the first.
Bury each generator pairing so that the fields will be nested, but each generator is within their respective bubble - not all in the innermost bubble, have a few in the spaces between the nested bubbles. And bury thoroughly - fill the second generator's force-fields with dirt or rubble, and make sure the floor is level throughout and is deep enough the curve of each force field above ground is a dome. Perhaps vary the dome levels a bit, how much is above or under ground, though they must fit entirely inside each other.
Once the floor is level, dig the foundation, pour a thick reinforced concrete foot, and build the building. Have lots of locks and traps, mechanisms for food, water, and waste, knockout gas, and a host of other mundane barriers to keep the teleporter from just walking out. Make sure there are locked doors just outside each layer of fore-field, and include rooms or areas in the layout he is simply locked out of (more decoys). Maybe a few electronic or generator decoys.
Get the teleporter in the prison, in the room covered by the innermost bubble. Try to make sure they don't have tools on hand, if putting them there - harder to do if luring them there, I'll admit. Turn on the layer generators, and lock the doors when leaving.
For the last, outermost level, don't pair it and don't bury it - make sure the dome just barely overlaps the roof, and tuck the generator in a locked structure between the roof and the top of the dome. Let him waste his time looking in the (very large) space underground for that last generator.
As a bonus, keep a few decoy boxes (with various running electronics), a few trap boxes, and even a few generators with minimum-sized fields (defunct or whole), and bury them all in the spaces between the actual generators.
This will take forever to get out of. He has "no special powers" - so even if he can somehow phase through solids... he can't see in the dark, he can't breathe without air, he has to figure out the locks and layers, one by one, to reach the generator, he has to figure out which bits would disable a force-field and which are decoys. He may get trapped in the second generator's force-field, which is completely full, if he teleported around to find the generator instead of digging it up - and then he can't see, can't breathe, might be physically trapped (if, say, he phased partway through and can't get back out).
He won't know how to access the generators, through layers of locks and traps, and if he eventually works through them he will have to figure out how to disable each one (even shallow variations can be a big problem if he can't see). And he may have difficulty negotiating the need to phase through things to reach, and the need to be solid to figure out and disable the thing, and the vulnerability of being solid when there are traps and things to injure or ward off.
And even if he eventually finds the first generators, he has to negotiate each layer, and their generators, and all the traps and such - including disabling generators and not seeing any result because it was for the next layer out or a decoy, or getting out but not finding the next layer's generator easily because he's only looking between but it was a few layers in. Coupled with decoy electronics, traps, and generators, he would take a long, long time to figure out which bits he needed and which were distractions.
And the last layer, well, having spent several layers with generators and a couple decoys underground, he would probably search the entire under-floor volume from one end to the next without realizing the force-field overlapped the roof, or that the generator might be above, rather than below, in this layer.
I would expect just three or four layers to take quite a bit of time to solve (months or years), and the potential for injuries or incapacitation (via traps, knockout gas, suffocation, or despair) to add more time still. More than enough time to add layers, or you can set up layers that would overlap the previous generator (auto-switching them on when the previous layer fails, so they don't actually overlap when active), or any number of things.