Non-biologist here stepping in.
@swbarnes2 has a good point pinning the fact that (approx) 3Giga nucleotides to display "on a wall" (as you state) even with a good projector is gonna be a hard task.
You'll need several projectors and a hell of a big wall.
(say you take the smallest readable police setting you'll have each letter take a space of 4*6 pixels which for the whole will bring you to ~[227k x 342k] pixels so around 35k HD-projectors)
Which led me to think of why you would want to do such a thing.
The most plausible of which is : it is for some sort of artistic/cultural intent.
In such case, rather than showing letters (ATGC) I recommend to encode it in binary (00,01,10,11) and make this value code for a colored pixel.
That will leave you with a square matrix of around 57k pixels edge (which remains humongous) of shaded in 4 tones black to white dots.
If you want to go even farther, trichromia stands to the rescue, don't make pixels code for just one nucleotide each.
Make them code for one "pseudo-codon" (triplet) each.
First nucleotide defining the red shade,
Second nucleotide defining the green shade,
last nucleotide defining the blue shade.
(plain and simple Additive color RGB stuff).
Knowing that the notion of codon is invalid and that any nucleotide (except the leading and trailing 2 of each chromosome) could be part of three distinct codon (depending on wether they are in an intron, exon or even alternatively spliced) we see that this grouping by 3 is not THAT right.
In such case why not take even more liberties ?
Group your nucletides by 12 (3 groups of 4) giving you more depths in the color shades.
-END OF EDITED SECTION-
you'll get a much nicer and significantly smaller matrix of [30k x 30k] (which is still gonna take you a big wall and a few HD-projectors ~150 but at this point you can compress the output with several methods and get merged pixels, yet 150 is far less than 35000).
I know I don't bring actual solutions to the asked question (but I really think @Omen did it pretty well) but I sensed that there maybe here some insight worth handing (at the risk of making a fool of myself)