ok keeping in mind its probably cheaper to buy a mattress and bed base than trying to make it i make my simple beds a bit different to uhms
i tend to make them with cupboards underneath for storage but heres an adaption for simplicity
assiming your matress is 4'6" by6'3" i use 6"x1" planed [dressed] timber for the frame 4x2" for the legs 2x1" for the battons the slats sit on and 4x1" for the slats now when you plane [dress ]timber you remove between 4 and 9mm in the process so [now i will talk metric
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2x1" finnishes up 22by 44mm 4x2" as 95x44mm 4x1" 96x44mm 6x1" 145x22mm
i make the frame 25mm bigger than the mattress so the sides will be [6'3"]1905mm +25mm+ 2x 22mm [to overlap the ends] 1974mm x2 sides
ends [4'6"] 1372 +25 = 1397 x2 ends
countersink and butt joint the sides to the ends with 4 screws per corner [use 10 by 2"] 5x50mm
the leggs are fixed 25mm from the top 'to work out the length of the legs you need to decide what you want under the bed!!!!
say you want to store 300mm high boxes you allow 25m for clearence 300+25+120 =445 [including overlap on sides]
secure the legs 25mm from the top with 2 50mm screws in the ends of the bed into the leg narrow side avoiding the top 50mm of the bed base which = the top 25mm of the leg and 25mm up
secure the side of the legs with 5 screws in a "W" patern 50mm down and 25mm up and 25mm in from the edge
measure down from the top 47mm batton under this line including battons on the long edge off the legs [ 8x1.5"] 4.5 x 35mm screws countersunk every 150mm screw and glued
cut a piece of 22x44 1395 long also 12 x 22x 145 and 2at 1305
countersink 2x [6x1.5] 3.5 x40mm screws 2 in each side of each slat
fix the short slats inbetween the legs each end then affix the slats using the 20by44 as a spacer and if you get to the end and the space is a bit big just affix the spacer in the gap
afix a furthe piece of 22by44mm timber 1875 long underneath the centre secured to each slat in turn using [6x1.5 "]3.5 by 40mm no need to countersink if you secure from underneath
sand all the exposed corners to take of the sharpness
bobs your uncle
wood from the sheds is in general poorer quality and comes out at between 18 and 19mm so is around 3mm thinner than wood yards