You know, dont OVER think it.Just DO it.
Draw a picture of how big you want it .
Put in each 2x4 for each side and size you need. and each piece of plywood so you know what to buy
Better to go 4ft or 8 ft as the wood is usually those lengths why waste it on an odd size..
If you cant hammer in a nail straight just buy star head screws ..cost more but too SIMPLE for anyone..Way less time and frustration.
Even I can do them
To go as cheap as you can...if you have time..
.Look for auctions AT houses ... they may have a pile of wood in the garage or some even may have a shed for sale.
The last one i went to late i found had had a "cat house" 6 ft tall went for $5.... Perfect for chickens!
Also if you have a just a few chickens you could even buy an big old tv cabinet for the coop.I saw one for $50 at an antique mall the other day.GOOD size.
Paint it a cute color and have an eclectic coop... less work
Also look a garage sales even antique stores for hinges windows.You can find an old time window for about $8-$16 Possible
ebay too or
ebay classified or craigs for all.
.Hinges are high the big ones are like $8 a piece at LOwes
My material for the coop from Lowes total about $240.I did reperpose some 2x4s and had 2 old windows i bought at antique malls.Building mine 8x4x6 I am in a hurry as i didnt plan ahead well so had to get it all now to be done for the chicks to go in at 5 weeks so did go to Lowes.. but am looking as i go for wood etc to use on a tractor coop.
If your wife wants it nice...paint it .Add wood edging to the doors windows in a different color helps cover the mistakes so makes it look finished.
And Each mistake is a lesson you wont forget again for the NEXT coop.