You may not even save money
Buying a pre built
Compared to building it yourself
Ie they may work out around same price
Or if its built to order you may have a build fee too
Recently built my stepson a £1500 budget pc
Pre built he looked at was £1500
Built it for him cost £1450
But the main difference was the components I picked
Though approximately equal in performance (some were better none were worse)
They had longer warranties 10 years on psu instead of 5
Longer warranties / TBW on the m2 drives
Longer warranty on gpu
And so on
Pre built they tend to emphasise the gpu and cpu
That's in them
Whereas the other components may be lesser quality
Than building it yourself
Even ocuk have a habit of shoving kolink psus in high cost builds
Instead of a 10 year warranty seasonic,bequiet etc
If its pre built yes you have a return to base warranty
But that means no pc for however long it takes
May just be a ram issue, gpu etc
With building your own you have the option of rma a single part
And shove a replacement in for the meantime
Should mean less downtime
As gray2233 said
If you give a budget some of the guys in here
Are great at giving you a part list
Ps.
Some builds on ocuk show 3-4 weeks build time
Though other companies they may actually be totally pre built
And ready to ship