This is "The Tunnel Under the World" by Frederik Pohl, from 1955--according to wikipedia, one of the first fictional example of mind uploading. Here's a part about the advertisers getting aggressive:
The car took a position in the middle of the block and stood silent
for a few minutes. Then there was a crackle from the speaker, and a
giant voice chanted:
"Feckle Freezers! Feckle Freezers! Gotta have a Feckle Freezer!
Feckle, Feckle, Feckle, Feckle, Feckle, Feckle—"
It went on and on. Every house on the block had faces staring out of
windows by then. The voice was not merely loud; it was nearly
deafening.
And here's a part about discovering his house was made of metal:
Where the old trunk had been, the cellar floor gleamed oddly bright.
He inspected it in the flashlight beam. It was metal!
"Son of a gun," said Guy Burckhardt. He shook his head unbelievingly.
He peered closer, rubbed the edges of the metallic patch with his
thumb and acquired an annoying cut—the edges were sharp.
The stained cement floor of the cellar was a thin shell. He found a
hammer and cracked it off in a dozen spots—everywhere was metal.
The whole cellar was a copper box. Even the cement-brick walls were
false fronts over a metal sheath!
And his boat:
The biggest surprise was the upside-down boat hull that blocked the
rear half of the cellar, relic of a brief home workshop period that
Burckhardt had gone through a couple of years before. From above, it
looked perfectly normal. Inside, though, where there should have been
thwarts and seats and lockers, there was a mere tangle of braces,
rough and unfinished.
The revelation you mentioned about the character's nature:
He said: "Oh. The explosion in my dream."
"It was no dream. You are right—the explosion. That was real and this
plant was the cause of it. The storage tanks let go and what the blast
didn't get, the fumes killed a little later. But almost everyone died
in the blast, twenty-one thousand persons. You died with them and that
was Dorchin's chance."
"The damned ghoul!" said Burckhardt.
The twisted shoulders shrugged with an odd grace. "Why? You were gone.
And you and all the others were what Dorchin wanted—a whole town, a
perfect slice of America. It's as easy to transfer a pattern from a
dead brain as a living one. Easier—the dead can't say no. Oh, it took
work and money—the town was a wreck—but it was possible to rebuild it
entirely, especially because it wasn't necessary to have all the
details exact.
And here he discovers the final twist you mention:
Burckhardt stood paralyzed. One of the moving mountains in the
blinding glare came toward him.
It towered hundreds of feet over his head; he stared up at its top,
squinting helplessly into the light.
It looked like—
Impossible!
The voice in the loudspeaker at the door said, "Burckhardt?" But he
was unable to answer.
A heavy rumbling sigh. "I see," said the voice. "You finally
understand. There's no place to go. You know it now. I could have told
you, but you might not have believed me, so it was better for you to
see it yourself. And after all, Burckhardt, why would I reconstruct a
city just the way it was before? I'm a businessman; I count costs. If
a thing has to be full-scale, I build it that way. But there wasn't
any need to in this case."
From the mountain before him, Burckhardt helplessly saw a lesser cliff
descend carefully toward him. It was long and dark, and at the end of
it was whiteness, five-fingered whiteness....
"Poor little Burckhardt," crooned the loudspeaker, while the echoes
rumbled through the enormous chasm that was only a workshop. "It must
have been quite a shock for you to find out you were living in a town
built on a table top."
