how to estimate repairs effectively

[Rod Coleman]

Estimating repairs is a difficult thing I've been doing research on it but there is no exact science. does anyone have any quick idea on how to estimate repairs.

my assumptions are

basic bathroom 4500 to 6000

kitchen 5000 to 7000

Roof 4500 to 7000

electrical upgrade  3500 to 5000

Hvac 4500 to 6000

Windows 200 to 350 a piece

re-doing entire plumbing  3500 to 5000

Please if you have an better idea people rein in on this, i am new and these are just assumptions.