I used 14", 16", 18" and 20" hair from Fashion Leader Hair, an aliexpress vendor I would buy from again and again! The hair I bought was body wave and in colours 4 (medium brown) and 1B (natural black). There was about 500g of hair in total and it has to be bleached to be dyed red, I used 40vol peroxide with blue dust free powder bleach, then dyed over that with Mellor and Russell Red Alert as its 99p for a box in Savers and I needed about 12 boxes to cover all the hair. To bleach and dye hair, you'll need foil to protect your surfaces, disposable gloves, mixing bowls and tinting brushes. All of this is available at your local beauty supply store, as well as discount stores like B&M, Homebargains, Poundland etc if you're in the UK, I'm sure if you're elsewhere in the world your discount stores will sell them too, and of course eBay is your friend!
I mixed the bleach and peroxide to a cake batter like consistency, saturated the hair in in, folded it in the foil for about 15 minutes. The hair being brown, and using 40 vol bleach, the hair didn't take long to process light enough to put the red on. After rinsing and leaving the hair to dry, I applied the red to the hair, then again rinsed and left to dry. I cut the wefts into approximately 10" strips to make it easier to sew in rows as well.
To construct a wig, you need first and foremost, a foam head. I got mine on eBay and used my camera tripod to hold the mannequin up. You also need a wig cap, needle and thread, scissors, berry pins and wig clips, I used 7. Again, all available from local beauty supply but I'm sure you can get them on eBay!
I used the berry pins to secure my wig cap to the mannequin head, but I did it inside out at first. I sewed my first 4 rows to the inside of the wig cap at the nape of the neck so that If I did want to wear the wig in a ponytail, you wouldn't see the under side of the cap.
When this was done, I carried on sewing wefts, starting with the longest length and working my way up to the shortest lengths. At this point my wig is starting to take shape. I used a loop method, where you push the needle through, and then loop the thread through itself. This makes it more secure, if you're unsure, this picture may explain better:
When I reached the top near where a closure would go, it looked like this:
I then took the cap off the stand and began cutting away the top of the cap. I then sewed the clips on the inside of the cap, which looked like this:
To put in a U part wig, you gather the hair around your parting, put it in a bun then begin french plaiting/cornrowing your hair underneath if you can, if not a bun should be fine. This just gives something for the clips to grip onto and keeps the underneath hair concealed. Then let down the hair in the bun, and style it over the wig so you can't see the part of the wig. One thing I will say is that this wig is very heavy and puts a lot of pressure on the hair. I wouldn't wear this all day every day, this is mainly for the use of one week on holiday, to give my hair a voluminous look and to save time. I also don't want to wear hair extensions all day but on the nights I will definitely benefit from putting this in quickly rather than separate wefts.