Almost a fifth of the price involves allowances. Allowances are not prices they are estimates. You will be expected to pay the actual cost of hiring an electrician and plumber which could be a far greater amount than estimated. Make sure the allowances are only for materials and subs; his labor should be in the base bid price. Ask if he will mark up materials and subs covered by allowances. You will need an exhaust fan with a duct to the outside. You didn't say where the project is located but you will probably have to provide heat for the space. It seems pretty obvious that this room will be used as a sleeping room so one or two hard wired smoke detectors will be needed. A carbon monoxide detector MUST be installed. I would guess the project will cost well over $20,000 not including what you buy unless the contractor is uninsured, and ignores licensing and permitting requirements. As for minimum space and height requirements, if the local code is based on the 2009 IRC, the 70 s.f. minimum floor space for a habitable space (bathrooms are not considered habitable spaces) includes the space where a sloped ceiling is 5 ft or higher and a level ceiling is 7 ft. or higher for a minimum of 50% of the required room floor area. The minimum height of a habitable room level ceiling is 7 ft and 5 ft at a sloped ceiling. A bathroom must have a ceiling height of 6-8 in front of each fixture. The required "means of egress" from all spaces in the house must be 3-0 wide for corridors and stairs and lead to an outside door without passing through a garage. Habitable attics and every sleeping room, in addition to a means of egress, must have an "emergency escape and rescue opening" of 5.7 s.f. (min. 24" high and 20" wide) with a max. sill height of 44" above the floor. You need to decide if the habitable space will be used as a sleeping space because the building inspector will either ask you or just assume it is one. As for insulation, some jurisdictions have different requirements for an existing structure which may be contained in the International Existing Building Code or state amendments to the IRC. Where I live the wall, floor and roof cavities must be filled with insulation equivalent to fiberglass batts however you might want more depending on your climate and cost of heating fuel. As for the structure, the framing seems fairly new so if it was really labeled as a "bonus" room on the original permit drawings it would have been designed for a habitable space load instead of a storage load. All of this should be covered by the tables in the building code so an engineer should not be needed unless the knee walls are intended to transfer rafter load to the floor joists. The worst case is you would need to open the garage ceiling to add some joists but it might be wise to open the ceiling anyway because the best way to seal the floor is to spray an inch or two of foam insulation from below, in fact I don't know of another way that works. Putting a sleeping room over a garage requires great care. I would have two CO detectors in the new space, one hard wired and one battery operated. CO is a dangerous killer. I would have lost a client if newly cut flowers had not wilted soon after delivery.

Love the dining set. I think a really simple rug will help frame the space. A large art piece would be a great idea. What do you think of these chandelier? Good Luck! [Currey & Company Metro Rectangular Chandelier[(https://www.houzz.com/products/currey-and-company-metro-rectangular-chandelier-prvw-vr~85329283) [Robert Abbey Jonathan Adler Meurice Chandelier, Deep Patina Bronze[(https://www.houzz.com/products/robert-abbey-jonathan-adler-meurice-chandelier-deep-patina-bronze-prvw-vr~5643071)

Built ins tend to take over a room. You can't take them with you when you move. They tend to make a room lean more traditional than modern--which your wainscoting already does--and will surely be more expensive than a media cabinet. My main objection to built ins is the Hobby Lobby junk they end up being filled with. Now, if you have lots of books and a collection of fine Ming vases or McCoy pottery or pre-Columbian artifacts, go for it. I stole this built in from your ideabook. It actually looks pretty good in your space and gives you lots of storage.

So I like how you have already created “zones” for your different activities. First, let’s talk paint. I like the blue. So in the areas where you have wainscoting, I’d paint it a medium blue gray. Where you have column bump puts, I’d paint those black or a dark charcoal gray. On all the other walls, I’d do the same medium blue/gray. I’d make the wall across for the sofas, the focal wall. I’d get the kids involved in this and have them come up with words that they feel represents their group and do a word graphic using vinyl lettering. If you can’t put the lettering directly on the wall, get some gator board and paint it the same color as the wall and put lettering on the gator board. Or an even less expensive option would be the let the kids paint the words on or use wide tip markers. Pick an accent color. I chose orange. Use it around the entrance door and then through the room. On the floor, I would get carpet squares like the ones I’m showing from Walmart, and do a pattern of orange, blue and gray but just in the seating area and the gaming area within the border of the vct. You may need to secure the edges with double stick carpet tape. String some Edison bulb lights. If your florescent lights are switched, turn one or two rows off so it’s not so bright. Add orange, grey and blue paper lanterns over you seating and gaming areas. Get black fitted tablecloths for your long tables. Add some gaming posters to the gaming area walls and you may consider getting high top tables for eating but also, not every one is comfortable sitting so close to someone else on a couch especially at this age. Check the restaurant section on Craistslist or your online yard sale sites.