Marking out a rectangle

[osca]

Hi
I am looking for some help in marking our a 10X12 rectangle for a shed. I want to lay it on blocks and use 3X3 treated timber to raise it off the ground but for some reason I cant get this layed out. The diagonals are always different. Is there an easy way to lay this out?
Any help would be appreciated before I go nuts

Thanks
Osca

 

[kevindgas]

given that 2 sides are the same and the other 2 sides are same

measure diagonally from top left to bottom right.
then do the same for top right to bottom left.

the two measurement will be equal when you have perfect rectangle

simples !

 

[stuart45]

Lay out the blocks on way and measure 8ft and mark it. Then lay out the other way and mark 6 ft. Check the diagonal is 10 ft. If not adjust the line of blocks. This will give you a square corner to work from. Or make a timber square.

 

[big-all]

just remember you only alter half the difference on diagonals

make youself up a large square
bit off wood 7ft long another 6ft and another bit 5ft long
lay the 7 and 6ft lengths in an "L "shape
mark the etreme outside edge of the 6ft at 3ft then the 7ft at 4ft [*]note below

when the gap between these 2 marks is exactly 5 ft they are square

the timber you choose must be dead strait and not likley to bend in use

use a triangle off ply to connect the corner and a further 2 braces along the length

[*] with the wood butted up together in the corner your 3 and 4 ft measures are taken from the point off the corner